Alternative electrode configurations for reduced power consumption

ABSTRACT

The disclosure describes devices and systems for determining alternative electrode combinations and power consumption for these alternative electrode combinations. In one example, a method includes identifying a set of one or more electrodes configured to deliver electrical stimulation therapy via a lead, determining, based on the set of one or more electrodes, one or more alternative electrode combinations for delivering electrical stimulation therapy, calculating, for each of the one or more alternative electrode combinations, a respective field similarity score with respect to the set of one or more electrodes, and outputting a representation of at least one of the one or more alternative electrode combinations for selection in at least partially defining electrical stimulation therapy, the representation comprising an indication of at least one of the respective power consumption values or the respective field similarity scores.

This application is a continuation of U.S. patent application Ser. No.15/143,245, entitled, “ALTERNATIVE ELECTRODE CONFIGURATIONS FOR REDUCEDPOWER CONSUMPTION,” which was filed on Apr. 29, 2016. The entire contentof U.S. patent application Ser. No. 15/143,245 is incorporated herein byreference.

TECHNICAL FIELD

The disclosure relates to electrical stimulation and, more particularly,selection of stimulation parameters for electrical stimulation therapy.

BACKGROUND

Implantable neurostimulation devices have been used to treat acute orchronic neurological conditions. Deep brain stimulation (DBS), the mildelectrical stimulation of sub-cortical structures, belongs to thiscategory of implantable devices, and has been shown to betherapeutically effective for Parkinson's disease, Dystonia, EssentialTremor, Obsessive Compulsive Disorder, and Epilepsy. New applications ofDBS in the domain of psychiatric disorders (clinical depression,anorexia nervosa, schizophrenia) are being researched. In some examplesystems, a lead carrying four ring electrodes at its distal portion isconnected to an implantable pulse generator to deliver electricalstimulation therapy.

SUMMARY

In general, the disclosure describes techniques, devices, and systemsfor determining alternative electrode combinations that may providereduced power consumption during stimulation therapy while maintainingappropriate stimulation fields. A user or system may identify a set ofone or more electrodes as a starting point or constraint for generationof different alternative electrode combinations. The identified set ofone or more electrodes may correspond to selected electrodes from auser, electrodes associated with a user selected set of stimulationparameters or system selected set of stimulation parameters, or even oneor more electrodes that correspond to an initial volume of tissuetargeted for activation by electrical stimulation. In one example, thesystem may receive an initial electrode combination (e.g., a set of oneor more electrodes from user input or from a selected set of stimulationparameters) that provides a desired or intended stimulation field (e.g.,a volume of neural activation, a volume of tissue activation, or anelectric potential distribution) to stimulate a specific anatomicalregion. The system may identify alternative electrode combinations thatmay provide stimulation therapy that consumes less power than the set ofone or more electrodes, or the initial electrode combination, butdeliver a stimulation field similar to the stimulation field deliverablewith the set of one or more electrodes.

For example, the system may determine alternative electrode combinationsthat are associated with a lower collective impedance than thecollective impedance associated with the set of one or more electrodesoriginally identified. The lower collective impedance may be due to thealternative electrode combinations having additional electrodes over aninitial electrode combination in order to reduce the impedance of theelectrodes and thus reduce the total power necessary to deliverstimulation at the same current level. In other examples, one or morealternative electrode combinations may include the same or fewerelectrodes than the initial electrode combination but include lowerresistance tissue across which stimulation current travels. The systemmay display, for an electrode combination selection by a user, arepresentation of the power consumption values and/or the similarity ofthe stimulation fields generated by the one or more alternativeelectrode combinations with respect to the stimulation field associatedwith the set of one or more electrodes (e.g., the initial electrodecombination) for one or more alternative electrode combination. In otherexamples, the system may automatically select an alternative electrodecombination according to the reduced power consumption values and/orsimilarity of the stimulation field.

In one example, the disclosure is directed to a method that includesidentifying, by one or more processors, a set of one or more electrodesconfigured to deliver electrical stimulation therapy via a lead, thelead comprising a plurality of electrodes arranged in a complexelectrode array geometry, wherein the plurality of electrodes comprisesthe set of one or more electrodes, determining, by the one or moreprocessors and based on the set of one or more electrodes, one or morealternative electrode combinations for delivering electrical stimulationtherapy, wherein each of the one or more alternative electrodecombinations are associated with a respective power consumption valuelower than a power consumption value associated with the set of one ormore electrodes, calculating, by the one or more processors and for eachof the one or more alternative electrode combinations, a respectivefield similarity score with respect to the set of one or moreelectrodes, and outputting, by the one or more processors, arepresentation of at least one of the one or more alternative electrodecombinations for selection in at least partially defining electricalstimulation therapy, the representation comprising an indication of atleast one of the respective power consumption values or the respectivefield similarity scores.

In another example, the disclosure is directed to a system that includesone or more processors configured to identify a set of one or moreelectrodes configured to deliver electrical stimulation therapy via alead, the lead comprising a plurality of electrodes arranged in acomplex electrode array geometry, wherein the plurality of electrodescomprises the set of one or more electrodes, determine, based on the setof one or more electrodes, one or more alternative electrodecombinations for delivering electrical stimulation therapy, wherein eachof the one or more alternative electrode combinations are associatedwith a respective power consumption value lower than a power consumptionvalue associated with the set of one or more electrodes, calculate, foreach of the one or more alternative electrode combinations, a respectivefield similarity score with respect to the set of one or moreelectrodes, and output a representation of at least one of the one ormore alternative electrode combinations for selection in at leastpartially defining electrical stimulation therapy, the representationcomprising an indication of at least one of the respective powerconsumption values or the respective field similarity scores.

In another example, the disclosure is directed to a non-transitorycomputer-readable medium that includes instructions that, when executed,cause one or more processors to identify a set of one or more electrodesconfigured to deliver electrical stimulation therapy via a lead, thelead comprising a plurality of electrodes arranged in a complexelectrode array geometry, wherein the plurality of electrodes comprisesthe set of one or more electrodes, determine, based on the set of one ormore electrodes, one or more alternative electrode combinations fordelivering electrical stimulation therapy, wherein each of the one ormore alternative electrode combinations are associated with a respectivepower consumption value lower than a power consumption value associatedwith the set of one or more electrodes, calculate, for each of the oneor more alternative electrode combinations, a respective fieldsimilarity score with respect to the set of one or more electrodes, andoutput a representation of at least one of the one or more alternativeelectrode combinations for selection in at least partially definingelectrical stimulation therapy, the representation comprising anindication of at least one of the respective power consumption values orthe respective field similarity scores.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages of the disclosure will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a conceptual drawing of an example neurostimulation system thatdelivers deep brain stimulation (DBS) according to the presentdisclosure.

FIGS. 2A, 2B, and 2C are schematic diagrams of an example thin film,lead, and probe of a neurostimulation system for DBS.

FIG. 3 is a conceptual drawing of an example system that delivers DBS.

FIG. 4 is a conceptual drawing of another example lead having a complexelectrode array geometry.

FIG. 5 is a functional block diagram of an example implantable medicaldevice (IMD) configured to couple to one or more leads.

FIG. 6 is a functional block diagram of an example external programmerfor an IMD.

FIG. 7 is a conceptual diagram of an example distributed system thatoperates over a network.

FIG. 8 is a conceptual diagram of example alternative electrodecombinations selected based on the distance of other electrodes to anelectrode of the initial electrode combination.

FIG. 9 is a conceptual diagram of example stimulation fields deliverablefrom alternative electrode combinations.

FIG. 10 is a flow diagram of an example process for determiningalternative electrode combinations according to the present disclosure.

FIG. 11 is a conceptual diagram illustrating an example monopolarstimulation circuit that represents a system impedance.

FIG. 12 is a conceptual diagram illustrating an example load model formultiple stimulation generators in a system.

DETAILED DESCRIPTION

As generally described herein, systems, devices, and methods maydetermine alternative electrode combinations from a set of one or moreelectrodes (e.g., an original electrode combination) to reduce powerconsumption of stimulation therapy delivery while maintaining similarstimulation fields. For most electrical stimulation therapies, certainelectrodes are selected in order to produce a stimulation field thataffects desired nerves or neurons. In the example of deep brainstimulation (DBS), one or more leads carrying a plurality of electrodesare implanted within the deep regions of the brain. A lead may include acomplex electrode array geometry, which may include electrodes atdifferent axial positions of the lead and electrodes at differentcircumferential locations around the circumference of the lead (if thelead is cylindrical in shape).

The clinical benefit of DBS may be dependent upon the spatialdistribution of the electric field in relation to one or more areas ofthe brain. Appropriate selection of electrodes may produce a stimulationfield that targets certain areas to maximize therapeutic benefits whileavoiding unwanted side effects that could occur if the stimulation fieldaffects other areas of the brain. In this manner, one or more electrodeson one side of the lead may be active while other electrodes on theother side of the lead may remain unused when delivering the stimulationsignal. Although fewer active electrodes may provide a more targetedstimulation field, fewer active electrodes and/or electrodes with highersurface resistivity at the tissue interface may also result in highersystem impedance for delivery stimulation therapy. Other systemvariables, such as certain electrical components (e.g., blockingcapacitors, cable resistances, current sources) in the circuitry, mayalso contribute to certain higher or lower impedances. This is becausethe power consumption P (e.g., watts) for the system (e.g., astimulation generator) is determined by the amount of current I (e.g.,total stimulation current, in amperes), its duration (e.g., stimulationpulse width, in seconds) and frequency (e.g., stimulation pulsefrequency, in Hz) that is driven through the collective load or systemimpedance Z (e.g., connected to the stimulation generator, in ohms). Inother examples, the collective load or system impedance may berepresented by only its resistance, Re(Z). The impedance used indetermining the power consumption may be the total impedance for theentire system (e.g., a collective impedance for a circuit that includesa specified electrode combination through which the electricalstimulation pulses are delivered), such as impedances corresponding tovarious electrical components, electrode-tissue interfaces, and thetissue as discussed in the example of FIG. 11 and FIG. 12. The impedancemay be measured or may be calculated from an electrical model of boththe system and electrodes. For a system using a constant current ofelectrical stimulation, fewer electrodes being used in the electrodecombination may generally increase the impedance, and the powerconsumption, of the system. Therefore, delivering electrical stimulationvia fewer active electrodes can reduce the battery longevity of theimplantable medical device (IMD) driving the system. As discussed above,electrodes with higher surface resistivity due to the tissue interfacemay also increase the effective impedance for certain electrode morethan other electrodes. An increase in power consumption can decrease theduration between re-charging sessions, decrease total battery longevityof the IMD, and potentially increase the frequency of surgeries requiredto replace IMDs at the end of battery life.

As described herein, a system identifies a set of one or more electrodesconfigured to deliver electrical stimulation therapy via a lead. Thisidentification may include identifying a user defined electrode orelectrode combination for stimulation, identifying one or moreelectrodes that can deliver a stimulation field desired (e.g., defined)by a user or selected by the system, or identifying one or moreelectrodes included in a set of stimulation parameters otherwiseselected for defining stimulation therapy. A set of stimulationparameters, as discussed herein, may define values for electrodecombinations, current or voltage amplitudes, pulse frequencies, pulsewidths, duty cycle, etc. In this manner, some stimulation parameters maydefine the pulses that are applied to tissue via the electrodecombination also defined by the set of stimulation parameters. In someexamples, a stimulation program may also define the set of stimulationparameters (e.g., signal characteristics and the electrode combinationthrough which the signal is delivered to tissue). The system may use theidentified set of one or more electrodes as a starting point, or as aconstraint, on the alternative electrode combinations available forconsideration. In one example generally described herein, the identifiedset of one or more electrodes may be an initial or original electrodecombination that the alternative electrode combinations are based on.However, in the examples described herein, the set of one or moreelectrodes may be used as a basis for determining alternative electrodecombinations instead of an initial electrode combination that thealternative electrode combinations are based on.

The system may also determine one or more alternative electrodeconfigurations that may reduce power consumption when compared to theset of one or more electrodes, such as an initial electrode combination,while providing a similar stimulation field to the stimulation field ofthe initial electrode combination. The initial electrode combination maybe selected by a user or otherwise identified (e.g., from a selectedstimulation program, as a starting point for the general direction ofstimulation from the lead, or as corresponding to a stimulation fielddesired by a patient) for delivery of electrical stimulation therapy.The initial electrode combination may include one or more electrodes andmay be configured to operate in unipolar or bipolar configurations. Theinitial electrode combination may include as few as one or twoelectrodes that are intended to focus, or steer, the stimulation fieldto a desired anatomical region of the brain. However, as discussedabove, few electrodes may increase the power consumption of the systemwhen delivering stimulation therapy.

The system may determine one or more alternative electrode combinationsthat may provide stimulation therapy that consumes less power than theinitial electrode combination but deliver a stimulation field similar tothe stimulation field deliverable with the initial electrodecombination. In this manner, the alternative electrode combinations mayhave respective collective impedances (i.e., a total impedance for astimulation signal delivered via the alternative electrode combination)that are lower than the collective impedance of the initial electrodecombination. For example, the system may add electrodes in closestproximity to the initial electrode combination to generate onealternative electrode combination. The system may continue to add thenext closest electrodes to iteratively determine additional alternativeelectrode combinations. The greater number of electrodes in thealternative electrode combinations may generally decrease the impedanceand power consumption of the system, but the corresponding stimulationfield may also be increasingly dissimilar to the stimulation field ofthe initial electrode combination. In some examples, an alternativeelectrode combination may have the same or fewer electrodes of theinitial electrode combination, but the electrodes of the alternativeelectrode combination may be associated with lower tissue impedancesthan the electrodes of the initial electrode combination.

The system may calculate a power consumption value and a fieldsimilarity score for each of the alternative electrode combinations.These calculations may provide objective indications of the performanceof each electrode combination based on modeling of the electrodecombinations. This modeling of the electrode combinations may includeresistance or impedance modeling of the electrodes (e.g., an R-matrix orZ-matrix, respectively) and/or electrical field modeling and/orelectrical potential distribution modeling, one, two, or all of whichmay be used to determine the electrical field, electrical potentialdistribution, volume of neuron activation (VNA), or volume of tissueactivation (VTA). Axon models of brain tissue, for example, may be usedto determine the VNA and VTA. In some examples, the system may present arepresentation of these objective measures, such as the powerconsumption values relative to the initial electrode combination, anumerical score indicating the similarity between stimulation fields ofeach alternative electrode combination and the initial electrodecombination, and/or a visual representation of the stimulation fieldsfor each alternative electrode combination. The system may be configuredto receive a user input selecting one of the alternative electrodecombinations for therapy. In other examples, the system mayautomatically select an alternative electrode combination. For example,the system may detect a loss of one or more electrodes (e.g., anelectrode failure, switch failure, or conductor failure that results inthe inability to deliver stimulation via an electrode) and initiate aprocess for selecting another electrode combination that includesavailable electrodes that provides similar power consumption and/orfield similarity scores to the previous electrode combination thatincludes the now unavailable electrode(s). This process may includere-calculating the resistance and/or the impedance matrix of theremaining electrodes. In some examples, the system may store previouslyselected rankings of alternative electrode combinations which do notinclude the unavailable electrodes and automatically select a newelectrode combination based on the previous ranking. The system may usethe selected alternative electrode combination with or without userconfirmation. In this manner, the system may use alternative electrodecombinations that can reduce the power consumed during stimulationtherapy while maintaining a similar stimulation field to that desired bya user.

Stimulation fields described herein may refer to different types offields, areas, or volumes associated with the delivery of electricalstimulation. In one example, a stimulation field may refer to a volumeof anatomy in which neural brain activity (in the example of deep brainstimulation) is modulated by the distribution of the stimulation pulsesdelivered from one or more electrodes of a stimulation lead. These typesof stimulation fields may, in some examples, be referred to as a volumeof neural activation (VNA) or volume of tissue activation (VTA). The VNAor VTA may be derived from simulations of the delivered electricpotential distribution from the lead together with computational axonmodels of various sizes and/or orientations. In another example, astimulation field may refer to the electric potential distribution orelectrical gradients thereof (e.g., an electric field and/or divergenceof the electric potential). In this manner, the stimulation fieldsdescribed herein may provide information in the context ofelectrostatics and/or stimulation therapy. Any of these or other typesof stimulation fields may be used to compare and/or select one or morealternative electrode combinations as described herein. In addition,each different type of stimulation field may be represented numericallyor graphically.

Electrical stimulation therapy is generally described as being deliveredto the patient in the absence of other therapies. However, the patientmay receive electrical stimulation therapy in addition to other types oftherapies such as drug delivery therapies (e.g., from the same orseparate implantable device), oral medications, physical therapies, orother therapies that may address the same, related, or differentconditions of the patient. The electrical stimulation therapy may beselected to work in concert with any of these therapies.

FIG. 1 a conceptual drawing of an example neurostimulation system 10that delivers deep brain stimulation (DBS) according to the presentdisclosure. In other examples, neurostimulation system 10 may bedirected to other applications such as spinal cord stimulation or pelvicfloor stimulation. Neurostimulation system 10 includes at least acontroller 14 (e.g., an implantable medical device (IMD) and/or a firstmodule comprising one or more pulse generators) that may be surgicallyimplanted in the chest region 3 of a patient 1, typically below theclavicle or in the abdominal region of patient 1. Controller 14 can beconfigured to supply the necessary stimulation pulses, e.g., in the formof current or voltage pulses (e.g., also referred to as a stimulationsignal) to lead arrangement 18. DBS system 100 may further include aconnecting cable 16 (e.g., an extension wire) connected to thecontroller 14 and running subcutaneously to the skull 2, such as alongthe neck 4, where it terminates at a connector for lead arrangement 18.

DBS lead arrangement 18 may be implanted in the brain tissue, e.g.,through a burr-hole in the skull. In some examples (e.g., as shown inFIGS. 2C and 3), DBS lead arrangement 18 may include one or more leadscoupled to at least one module including a switch matrix. In thismanner, the switch matrix may be included in a second module 111 that isseparate from controller 14. In addition, DBS system 100 may include oneor more grounding electrodes. The grounding electrodes may be carried byconnecting cable 16, for example, between controller 14 and leadarrangement 18. In some examples, connecting cable 16 may be formed bytwo or more cables configured to connect to each other in parallel, andone or more of these cables may carry a grounding electrode.

Lead arrangement 18 may include a plurality of electrodes arranged in acomplex electrode array geometry. A complex electrode array geometrygenerally refers to an arrangement of stimulation electrodes at multiplenon-planar or non-coaxial positions, in contrast to simple electrodearray geometries in which the electrodes share a common plane or acommon axis. An example of a simple electrode array geometry is an arrayof ring electrodes distributed at different axial positions along thelength of a cylindrical lead. Another example of a simple electrodearray geometry is a planar array of electrodes on a paddle lead.

An example of a complex electrode array geometry, in accordance withthis disclosure, is an array of electrodes positioned at different axialpositions along the length of a lead, as well as at different angularpositions about the periphery, e.g., circumference, of the lead. In someexamples, electrodes in the complex electrode array geometry may includetwo or more electrodes (e.g., two, three, four, or more electrodes) atone axial position along the lead. This may be referred to as a “level”of the lead. The lead may also include two or more levels, whereas eachlevel includes multiple electrodes at different angular positions. Insome examples (e.g., electrodes 28 shown in the example of FIG. 2A),electrodes at one level may be staggered circumferentially withelectrodes of an adjacent level. In other examples (e.g., electrodes oflead 60 in FIG. 4), electrodes at one level may be alignedcircumferentially with electrodes of an adjacent level.

In some examples, the electrodes in the complex electrode array may becircular, rectangular, or non-rectangular areas of conductive materialdeposited at respective locations. In other examples, the electrodes inthe complex electrode array geometry may appear similar tonon-contiguous, arc-like segments of a conventional ring electrode. Alead with a complex electrode array geometry may include multiple“rings” of such electrode segments. Each ring is disposed at a differentaxial position. Each electrode segment within a given ring is disposedat a different angular position. The lead may be cylindrical or have acircular cross-section of varying diameter. Another example of a complexelectrode array geometry is an array of electrodes positioned onmultiple planes or faces of a non-circular lead. As an illustration,arrays of electrodes may be positioned on opposite planes of a paddlelead or multiple faces of a lead having a polygonal cross-section.

External programmer 20 wirelessly communicates with controller 14 asneeded to provide or retrieve therapy information. Programmer 20 is anexternal computing device that the user, e.g., a clinician and/orpatient 1, may use to communicate with controller 14. Programmer 20 maydetermine alternative electrode configurations and/or receive userselection of an alternative electrode configuration in order to reducepower consumption of the stimulation therapy, as described herein. Inone example, programmer 20 may be a clinician programmer that theclinician uses to communicate with controller 14 and program one or moretherapy programs for controller 14. Alternatively, programmer 20 may bea patient programmer that allows patient 1 to select programs and/orview and modify therapy parameters. The clinician programmer may includemore programming features than the patient programmer. In other words,more complex or sensitive tasks may only be allowed by the clinicianprogrammer to prevent an untrained patient from making undesirablechanges to controller 14.

When programmer 20 is configured for use by the clinician, programmer 20may be used to transmit initial programming information to controller14. This initial information may include hardware information, such asthe type of leads and the electrode arrangement, the position of leadswithin the brain of patient 1, the configuration of an electrode array(e.g., electrodes 132 of FIG. 2A), initial programs defining therapyparameter values such as selected electrode configurations, and anyother information the clinician desires to program into controller 14.

The clinician may also store therapy programs within controller 14 withthe aid of programmer 20. During a programming session, the clinicianmay determine one or more therapy programs that may provide efficacioustherapy to patient 1 to address symptoms associated with the patientcondition. For example, the clinician may select one or more stimulationelectrode combinations with which stimulation is delivered to the brain.In some examples, programmer 20 may determine and present alternativeelectrode configurations that may consume less power during therapyand/or receive user input selecting one of the alternative electrodeconfigurations. During the programming session, patient 1 may providefeedback to the clinician as to the efficacy of the specific programbeing evaluated or the clinician may evaluate the efficacy based on oneor more physiological parameters of patient 1 (e.g., muscle activity ormuscle tone). Programmer 20 may assist the clinician in thecreation/identification of therapy programs by providing a methodicalsystem for identifying potentially beneficial therapy parameter values.

Programmer 20 may also be configured for use by patient 1. Whenconfigured as a patient programmer, programmer 20 may have limitedfunctionality (compared to a clinician programmer) in order to preventpatient 1 from altering critical functions of controller 14 orapplications that may be detrimental to patient 1. In this manner,programmer 20 may only allow patient 1 to adjust values for certaintherapy parameters or set an available range of values for a particulartherapy parameter.

Neurostimulation system 10 may be implemented to provide chronicstimulation therapy to patient 1 over the course of several months oryears. However, system 10 may also be employed on a trial basis toevaluate therapy before committing to full implantation. If implementedtemporarily, some components of system 10 may not be implanted withinpatient 1. For example, patient 1 may be fitted with an external medicaldevice, such as a trial stimulator, rather than controller 14. Theexternal medical device may be coupled to percutaneous leads or toimplanted leads via a percutaneous extension. If the trial stimulatorindicates DBS system 10 provides effective treatment to patient 1, theclinician may implant a chronic stimulator within patient 1 forrelatively long-term treatment. In addition, or alternative, todelivering stimulation therapy, system 10 may record neurologicalactivity using one or more of the electrodes carried by lead assembly18.

As described herein, system 10 may perform one or more processes inorder to use an alternative electrode combination that may reduce powerconsumption of electrical stimulation therapy. Programmer 20 may performthis process in some examples, controller 14 may perform this process inother examples, or a combination of programmer 20 and controller 14 mayperform these processes in other examples in a form of distributedcomputing. Alternatively, one or more networked servers may be employedto perform one or more steps of the processes described herein.

In one example, programmer 20 may, using one or more processors, receivean indication of a first electrode combination for delivering electricalstimulation therapy via a lead (e.g., lead assembly 18) that includes acomplex electrode array geometry. The first electrode combination may bean initial electrode combination that defines one or more electrodes ofthe complex electrode array geometry as being active for deliveringstimulation therapy. In some examples, a user (e.g., patient 1 or aclinician) may define the initial electrode combination in order totarget a desired anatomical region of the brain. In other examples,programmer 20 may select or identify the initial electrode combinationbased on a user-selected program, desired anatomical region to receivestimulation therapy, or a condition to be treated. In this manner, theinitial electrode combination may be a set of one or more electrodesthat correspond to a VNA or VTA that covers and/or fills the desiredanatomical region or area with respect to the lead to receivestimulation therapy.

Programmer 20 may then determine, based on the first electrodecombination, one or more alternative electrode combinations fordelivering electrical stimulation therapy. Each of the one or morealternative electrode combinations may include a greater number ofelectrodes than the first electrode combination. In some examples, allof the alternative electrode combinations include the electrode(s) ofthe first electrode combination, but in other examples the firstelectrode combination may not always be included in each alternativeelectrode combination.

For each of the one or more alternative electrode combinations,programmer 20 may calculate or measure respective power consumptionvalues and respective field similarity scores with respect to a set ofone or more electrodes, which may be a first electrode combination asdescribed herein in some examples. In this manner, programmer 20 maycompare the alternative electrode combinations to one or more aspects ofthe set of one or more electrodes. Programmer 20 may then generate andoutput a representation of at least one of the one or more alternativeelectrode combinations for selection in at least partially definingelectrical stimulation therapy. The electrode combinations may bedescribed as “partially defining” electrical stimulation therapy becauseadditional stimulation parameters, such as current or voltage amplitude,pulse width, pulse frequency, etc., may also contribute to defining theelectrical stimulation received by the patient. The representation mayinclude an indication of at least one of the respective powerconsumption values and the respective field similarity scores for the atleast one alternative electrode combination. This representation may beused to indicate what alternative electrode combination wasautomatically selected or to present information that the user canreview prior to selecting the desired alternative electrode combination.

In some examples, programmer 20 may determine the one or morealternative electrode combinations by iteratively determining each ofthe one or more alternative electrode combinations such that successivealternative electrode combinations add one or more electrodes to allelectrodes defined by prior alternative electrode combinations. In otherwords, programmer 20 may determine the alternative electrodecombinations via generating different generations of electrodecombinations. For example, programmer 20 may start with the initialelectrode combination and then add one or more closest availableelectrodes to for an alternative electrode combination. The closestavailable electrodes may include all of the electrodes at the samedistance, or equidistant, from the one or more electrodes of the initialelectrode combination. Additional alternative electrode combinations maycontinue to be determined by adding the next closest availableelectrodes. Thus, successive alternative electrode combinations, orfurther generations, include electrodes at increasing distances from oneor more electrodes of the first electrode combination. In otherexamples, programmer 20 may perform an exhaustive search for alternativeelectrode combinations that satisfy constraints that may be based on theinitial electrode combination. In some cases, one or more alternativeelectrode combinations may have fewer electrodes than the initialelectrode combination, but the fewer electrodes may be associated withlower impedances that may be due to adjacent tissue having lowerresistance than the tissue surrounding electrodes of the initialelectrode combination. In this manner, a first alternative electrodecombination of the one or more alternative electrode combinations mayinclude a first number of electrodes less than or equal to a secondnumber of electrodes of the initial electrode combination, and a firstpower consumption value associated with the first alternative electrodecombination is less than a second power consumption value associatedwith the initial electrode combination.

Programmer 20 may also generate information that allows each alternativeelectrode combination to be compared to the initial electrodecombination. This information may be based on power consumption valuesand stimulation fields for each electrode combination. For example,programmer 20 may calculate respective power consumption values bycalculating, for each of the set of one or more electrodes (e.g., afirst electrode combination) and the one or more alternative electrodecombinations, the power dissipated in a respective system impedanceassociated with the respective electrode combination (i.e., a systemimpedance or collective impedance) for a set of common stimulationparameters (e.g., stimulation amplitudes, pulse widths, pulsefrequencies etc.). The power dissipation may be determined using anR-matrix, Z-matrix, and/or an electrical model of system 10 that is usedto deliver electrical stimulation using a common set of stimulationparameters (for different electrode combinations in some examples),different sets of stimulation parameters (for the same electrodecombinations in some examples), or different sets of stimulationparameters for different electrode combinations. For example, the commoncurrent value may be a stimulation current of 1.5 milliamps (mA),although lower or higher current values may be used. The common currentvalue may be selected based on currents intended for use on theparticular patient. In some examples, different currents, pulse widths,pulse frequencies etc. may be used for different electrode combinations.The power consumption value described herein may refer to an averagepower consumption value that takes into account pulse delivery times,non-pulse delivery times, and pulse frequency. Therefore, the powerconsumption value may take into account the pulse width, or duty cycle,and the frequency of the delivered pulses and generate the powerconsumption value to reflect the power used over any given cycle ofstimulation delivery. In other examples, an “energy consumption value”per unit of time may be used to reflect this average power consumption.In any case, programmer 20 may thus use the stimulation parameters tocalculate the respective power consumption value for each electrodecombination (e.g., for comparison purposes). The collective impedance ofeach electrode combination may be calculated based on known or measuredimpedances of system electrical components, electrode-tissue interfaces,and tissue resistance (e.g., from a known or measured R-matrix orZ-matrix). Example contributing elements are described in FIG. 11 andFIG. 12. In other examples, power monitor 109 of FIG. 5, for example,may be used to measure actual power consumption of one or more electrodecombinations.

In some examples, the resistance, or impedance, of each electrode in thecomplex electrode array geometry of the lead (e.g., lead assembly 18)may change over time. Electrodes may become encapsulated in tissues ofvarious densities and/or shift slightly over time. Therefore, thetissue/electrode interface may be altered over time and the effectiveimpedance of tissue, and each electrode used in an electrodecombination, may change. Controller 14 may periodically, or uponcommand, measure the impedance of each electrode of the lead or thecomplete resistance or impedance matrix (e.g., R-matrix or Z-matrix) ofthe lead. Programmer 20 may thus use the most recent measured impedancevalues for the electrodes when calculating the overall impedance of theinitial and/or alternative electrode combinations. In some examples,programmer 20 may periodically, upon command, or in response to detectedincreases in power consumption, re-calculate alternative electrodecombinations during the life of system 10 in order to maintainefficiency energy usage by system 10.

When presenting the alternative electrode combinations to a user,programmer 20 may rank the alternative electrode combinations based onthe respective power consumption value such that the representation ofat least some of the one or more alternative electrode combinations isindicative of the ranking. For example, programmer 20 may rank thealternative electrode combinations according to reduced energyconsumption. The ranking may include the initial electrode combinationas well. The power consumption values may be an absolute amount ofenergy used per unit time, a percentage of energy used when compared tothe initial electrode combination, or a percentage of energy savings ascompared to the initial electrode combination. In one example, the powerconsumption may be calculated using resistances or impedances determinedusing the R-matrix or Z-matrix approach, as discussed further below inrelation to FIG. 12. In some examples, the power consumption values maybe represented by the amount of time the battery of controller 14 willlast before recharging when using the respective electrode combination.

Programmer 20 may also calculate a field similarity score for each ofthe alternative electrode combinations as a comparison to thestimulation field of the initial electrode combination. For example,programmer 20 may determine an original stimulation field deliverable bythe initial electrode combination and determine, for each of thealternative electrode combinations, a respective stimulation fielddeliverable by the respective alternative electrode combination.Programmer 20 may then compare, for each of the alternative electrodecombinations, the respective stimulation field deliverable by therespective alternative electrode combination to the original stimulationfield deliverable by the first electrode combination. Programmer 20 maythen output, for each of the alternative electrode combinations, anindication of the comparison

In some examples, the field similarity score may be a numericalrepresentation of how similar the stimulation field of the initialelectrode combination is to the stimulation field of an alternativeelectrode combination. Programmer 20 may compare the volumes of eachstimulation field and represent the field similarity score as the ratioof the two volumes. As another example, a field similarity score mayindicate a percentage of the volume of the original stimulation fieldthat overlaps with, or would share a same volume in space as, arespective stimulation field of an alternative electrode combination.Alternatively, a score may indicate a percentage of the volume of astimulation field of an alternative electrode combination that overlapswith, or would share a same volume in space as, the original stimulationfield. The field similarity score may be derived based on how two 3-Dstimulation field volumes in space compare to one another (e.g., howthey overlap). Alternatively, a field similarity score may indicate howone or more 2D representations of a first stimulation field compare tocorresponding 2D representations of another stimulation field. Othercomparison mechanisms may also be used to derive a field similarityscore.

In another example, programmer 20 may calculate the field similarityscore based on a Sorensen-Dice coefficient between the originalstimulation field and the respective stimulation fields deliverable bythe respective alternative electrode combinations. The Sorensen-Dicecoefficient may be used to assess the similarity between two samples(e.g., stimulation fields) and may be calculated according to:

$\begin{matrix}{{QS} = \frac{2{{A\bigcap B}}}{{A} + {B}}} & (1)\end{matrix}$where QS is the quotient of similarity with range [0, 1] with 1 being anidentical match; A and B are the number of species in samples A and B.In one example, A and B may be the volume elements of the stimulationfield of the initial electrode combination and the stimulation field ofthe respective alternative electrode combination. Any other metric thatdescribes how one field is similar to (e.g., overlaps or coincides with)another field may be used in the alternative to derive a fieldsimilarity score.

In addition, or in alternative, to presenting the field similarityscore, programmer 20 may output, for each of the first electrodecombination and at least one of the one or more alternative electrodecombinations, a visual representation of a stimulation field deliverablevia the respective electrode combination. The visual representation maybe a two dimensional (2D) graphical representation of the stimulationfield and/or a three dimensional (3D) graphical representation of thestimulation field. The 2D representation may be shown one or moredifferent views of the stimulation field, such a view along an axis ofthe lead and a side view orthogonal to the axis of the lead. Programmer20 may provide the user to interact with the 3D representation and turnor move the 3D representation in space. In some examples, programmer 20may display a distance grid or measurement markers on the stimulationfield to allow the user to visualize differences in sizes of eachstimulation field.

As discussed herein, programmer 20 may automatically select analternative electrode combination based on appropriate metrics, such aspreference given to reduced power consumption or the field similarityscore. Alternatively, programmer 20 may present the informationassociated with each alternative electrode combination for user reviewvia a user interface of programmer 20. Programmer 20 may then receive,via the user interface, a selection of one of the alternative electrodecombinations and control delivery of electrical stimulation therapy to apatient according to the selected alternative electrode combination. Forexample, programmer 20 may generate one or more therapy programs thatincorporate the selected alternative electrode combination for deliveryof electrical stimulation therapy. In this manner, programmer 20 maycontrol an IMD to deliver stimulation using the selected electrodecombination. Programmer 20 may then transmit the therapy program (oronly some stimulation parameters such as the selected electrodecombination) to controller 14 to define stimulation therapy. An IMD,such as controller 14, may thus be configured to receive the selectedalternative electrode combination and deliver the electrical stimulationtherapy according to the selected alternative electrode combination.

The examples generally described herein are related to selecting one ormore alternative electrode combinations for stimulation therapy in orderto reduce power consumption while retaining field similarity to achievea desired therapeutic outcome. In other examples, the processesdescribed herein may be relevant to the selection of any stimulationparameters (e.g., current or voltage amplitude, pulse frequency, pulsewidth, duty cycle, monopolar or bipolar configurations, etc.) in orderto determine other sets of stimulation parameters (e.g., one or morestimulation programs) that consume lower levels of power while alsodelivering stimulation fields providing therapeutic efficacy. Forexample, the system or a user may provide one or more constraints in theselection of stimulation parameters, such as which electrodes to use,which electrodes to avoid, desired current or voltage amplitudes,desired pulse frequency, desired pulse width and/or duty cycle, and/orVNA or VTA that is desired or to be avoided. Using these constraints,the system may automatically generate sets of stimulation parametersthat satisfy these constraints and rank the sets of stimulationparameters by power consumption values and/or field similarity scores.The system may incorporate tissue resistances and various systemresistances and/or impedances when calculating the power consumptionvalues for each of these sets of stimulation parameters. In this manner,the system may generate sets of stimulation parameters without basingthe parameters on an initial set of electrodes or initial electrodecombination.

Example constraints for selection of stimulation parameters may includea request for a certain number of lowest power consuming sets ofstimulation parameters that include electrodes no more than a certaindistance (or number of electrodes) from a desired circumferentialposition on the lead. The system may require a certain constraints inorder to generate usable stimulation parameters, such as minimums ormaximums for one or more of current, voltage, pulse width, frequency,number of electrodes, volume of activated tissue, etc. These constraintsmay be defaults set by the system and/or user definable. Other exampleconstraints may be a request for the lowest power consuming rings ofelectrodes, or lower power consuming electrode combinations andstimulation parameters with electrodes falling within a defined area ofthe lead. Constrains for stimulation field profiles, depth of tissueactivation from the lead, or any other therapeutic constraints may alsobe used or even required to perform the request.

FIGS. 2A, 2B, and 2C are schematic diagrams of an example thin film,lead, and probe of a neurostimulation system 10 for DBS. For example,FIG. 2A illustrates an example, thin film 24, FIG. 2B illustrates anexample DBS lead 22, and FIG. 2C illustrates an example lead assembly 18(e.g., a DBS probe) that include DBS lead 22 and a second module 17(e.g., an active lead can (ALC) separate from controller 14). Secondmodule 17 may include electronic means, such as a switch matrix, foraddressing electrodes 28 disposed on the distal end 32 of the thin film24. Electrodes 28 may be arranged at the distal end 42 of lead 22 andnext to the distal tip 44 of the DBS lead 22. Electrodes 28 may be anexample of a complex electrode array geometry with multiple levels ofelectrodes that are staggered in the circumferential direction. Althoughelectrodes 28 include 18 electrodes, fewer or greater numbers ofelectrodes may be carried by lead 22. In one example, lead 22 mayinclude 40 electrodes.

Lead 22 may include a carrier 38 for thin film 24. Carrier 38 may besized and shaped to providing the mechanical configuration of DBS lead22 and the thin film 24. In other words, thin film 24 may be wrappedaround the circumference or diameter of carrier 38. Thin film 24 mayinclude at least one electrically conductive layer and may beconstructed of a biocompatible material. The thin film 24 may beassembled to carrier 38 and further processed to constitute lead 22.

The thin film 24 for a lead may be formed by a thin film product havinga distal end 32, a cable 30 with metal tracks, and a proximal end 36.Proximal end 36 of the thin film 24 may be arranged at the proximal end40 of lead 22 and is electrically connected to the second module 17. Thesecond module 17 may include the switch matrix of the DBS steeringelectronics that selects different electrode combinations (e.g., selectswhich one or more electrodes are actively delivering an electricalsignal) from electrodes 28. The distal end 32 comprises electrodes 28for brain stimulation, for example. Proximal end 36 of thin film 24includes interconnect contacts 34 for each metal track in the cable 30.The cable 30 comprises metal tracks or lines (not shown) to electricallyconnect each of distal electrodes 28 to a respective and designatedproximal interconnect contact 34.

Second module 17 may include a switch matrix, or multiplexer, that isused to couple, or decouple, each electrode of electrodes 28 to one ormore pulse generator lines and ground provided to second module 17 via aconnecting cable (e.g., connecting cable 16 of FIG. 1 or 3). Secondmodule 17 may also be electrically coupled to one or more groundelectrodes. In some examples, second module 17 may include other controlelectronics, such as a microprocessor or other integrated circuitry,resistors, and capacitors. In still other examples, second module 17 mayinclude one or more signal generators (e.g., one or more pulsegenerators) that are provided in addition to, or instead of, one or moreof the pulse generators provided by controller 14. In other examples,the components of second module 17 may be incorporated into the housingof controller 14 such that a separate second module 17 is not necessarybetween controller 14 and electrodes 28.

FIG. 3 is a conceptual drawing of an example system 10 that deliversDBS. System 12 is described for brain applications, such asneurostimulation and/or neurorecording as a deep brain stimulationsystem 12 as shown in FIG. 1. System 12 may include at least one leadassembly 18 (e.g., a probe) for brain applications with stimulationand/or recording electrodes 28. In one example, forty electrodes 28 canbe provided on the outer body surface at the distal end of the leadassembly 18. Controller 14 (e.g., a first module) may include one ormore pulse generators that generate and supply neurostimulation pulses Pto a second module 17 (e.g., an active lead can) by means of theconnecting cable 16. A switch matrix of the second module 17 may directthe neurostimulation pulses P to the appropriate one or more electrodes(e.g., the electrode combination) for delivery to a patient. In someexamples, controller 14 can be or include an implantable pulsegenerator. In other examples, controller 14 may be configured tosimultaneously couple to two or more different second modules 17 andrespective lead assemblies 18 via one or more connecting cables 16.

In the example of FIG. 3, system 12 may include controller 14 (e.g., afirst module) that includes one or more pulse generators. Controller 14may also include components such as a power supply, one or moreprocessors, a memory, a communication unit for transmitting and/orreceiving information from an external device, and other components.Second module 17 may include a switch matrix and, in some examples, oneor more processors, a memory, and connectors for coupling lead 22 ofFIG. 2 (where lead assembly 18 may include second module 17 and lead 22carrying electrodes 28) and connecting cable 16. Second module 17 mayhave a housing encompassing the control electronics such as the switchmatrix. In some examples, the housing may be electrically nonconductivesuch as an epoxy or polymer that insulates and protects the componentsof second module 17. The electrically nonconductive material may reduceencapsulation of the housing and/or insulate the brain from anyinterference caused by the components of second module 17.

Connecting cable 16 may connect controller 14 to second module 17. Theplurality of electrodes 28 are disposed distal of second module 17 andon lead 22 of lead assembly 18. The control electronics for theplurality of electrodes 28 and the grounding electrode may provide atleast one of neurostimulation and/or neurorecording via at least oneelectrode of the plurality of electrodes 28 and the grounding electrode.The control electronics are arranged in at least the first module 14 andthe second module 17, but one or more additional modules may alsoinclude at least some of the control electronics. As described in FIG.2A, lead assembly 18 may include lead 22 constructed of a thin film 24carrying the plurality of electrodes 28. Lead 22 may be electricallycoupled to the switch matrix of second module 17.

FIG. 4 is a conceptual drawing of another example lead 60 having acomplex electrode array geometry. Lead 60 may be an alternative medicallead to lead 22 of FIGS. 2B and 3. Lead 60 includes distal end 62showing a plurality of electrodes 66A-C, 68A-C, 70A-C, and 72A-C. Asshown in FIG. 4, lead body 64 of lead 60 may be tubular in form and mayhave a substantially circular cross-section. However, lead body 64 oflead 60 may have any cross-sectional shape, such as rectangular,triangular, or other polygonal cross-sectional shapes in other examples,which may vary over the length of lead 60. An outer surface of lead body64 may be formed from a biocompatible material such as, for example,polyurethane or silicone.

Distal portion 62 of lead 60 also includes segmented electrodes 66A-C(collectively “electrodes 66”), segmented electrodes 68A-C (collectively“electrodes 68”), 70A-C (collectively “electrodes 70”), and 72A-C(collectively “electrodes 72”). Each of electrodes 66, 68, 70, and 72are levels of electrodes disposed at respective axial positions on leadbody 64. Electrodes 66C, 68C, 70C, and 72C are located on thecircumferential portion of lead 60 that is on the opposite side from thevisible side of lead 60 in FIG. 4. The approximate locations ofelectrodes 66C, 68C, 70C, and 72C are outlined with dotted lines.

Electrodes 66, 68, 70, and 72 do not extend substantially around theentire periphery of the lead body 64. Each of electrodes 66, 68, 70, and72 in the respective levels extend through arcs of 60 degrees, 80degrees, 90 degrees, or as many as 119 degrees, although lesser orgreater arcs may be used in other examples. Electrodes 66, 68, 70, and72 in each respective level may be, but need not be, evenly spacedaround the periphery of lead 60. Each of electrodes 66, 68, 70, and 72can be made from an electrically conductive, biocompatible material,such as platinum iridium. In addition, one or more of 66, 68, 70, and 72may function as sensing electrodes that monitor internal physiologicalsignals of patient 1 (FIG. 1).

In the illustrated embodiment, lead 60 includes four levels of segmentedelectrodes 66, 68, 70, and 72, respectively. Each level of electrodesincludes an electrode circumferentially aligned with respectiveelectrodes in other levels. For example, electrodes 66A, 68A, 70A, and72A are all circumferentially aligned with each other and at differentaxial positions on lead 60. However, in other examples, electrodes ofdifferent levels may be staggered, or not circumferentially aligned.Although each level includes three electrodes, a level of segmentedelectrodes may include two, four, five, six, or even more electrodesdisposed at the same axial position. Example lead 60 includes fourlevels of electrodes, but fewer levels such as one, two, or three ormore levels such as five, six, or more can be used in other examples.Each level may have the same number of segmented electrodes, but inother examples, different levels may have different number ofelectrodes.

In one example, lead 60 may include one or more ring electrodes incombination with one or more levels of multiple segmented electrodes.Ring electrodes may extend substantially around the entire periphery oflead 60. In some examples, multiple segmented electrodes may be usedtogether as a ring electrode because they are configured to provide astimulation field substantially similar to a full ring electrode. Insome embodiments, the distances between each of the axial positions ofeach level (e.g., the positions of the levels of electrodes 66, 68, 70,and 72) may be approximately equal. However, the axial distance betweenelectrodes may be varied between different levels of electrodes in otherexamples. Further, in some embodiments, although not illustrated in FIG.4, lead 60 may be coupled to controller 14 (FIG. 1) or IMD 100 (FIG. 5)directly or via one or more lead extensions.

FIG. 5 is a functional block diagram of an example IMD 100 configured tocouple to one or more leads 60. IMD 100 may be similar to controller 14of FIG. 1 and may include at least some functionality of second module17 (FIG. 3), however, second module 17 may not be located separate fromIMD 100. Each of these modules include electrical circuitry configuredto perform the functions described herein. In the example shown in FIG.5, IMD 100 includes processor 102, memory 114, stimulation generator108, power monitor 109, measurement module 111, sensing module 106,switch module 110, telemetry module 104, sensor 112, and power source122. Memory 114 may include any volatile or non-volatile media, such asa random access memory (RAM), read only memory (ROM), non-volatile RAM(NVRAM), electrically erasable programmable ROM (EEPROM), flash memory,and the like. Memory 114 may store computer-readable instructions that,when executed by processor 102, cause IMD 100 to perform variousfunctions. Memory 114 may be a storage device or other non-transitorymedium.

In the example shown in FIG. 5, memory 114 stores therapy programs 116and configuration instructions 118 in common or separate memories orareas within memory 114. Each stored therapy program 116 defines aparticular set of electrical stimulation parameters (e.g., a therapyparameter set), such as a stimulation electrode combination, electrodepolarity, current or voltage amplitude, pulse width, and pulse rate. Insome examples, individual therapy programs may be stored as a therapygroup, which defines a set of therapy programs with which stimulationmay be generated. The stimulation signals defined by the therapyprograms of the therapy group may be delivered together on anoverlapping or non-overlapping (e.g., time-interleaved) basis.

Configuration instructions 118 may include rules, algorithms, data, orany other information related to determining alternative electrodecombinations, calculating power consumption values and stimulation fieldsimilarity scores, and selecting an alternative electrode combinationfor therapy. For example, configuration instructions 118 may include oneor more algorithms defining how to generate different alternativeelectrode combinations based on an initial electrode combination.Configuration instructions 118 may also include instructions regardingwhether processor 102 should automatically select an alternativeelectrode combination or present alternative electrode combinations to auser for selection. In some examples, configuration instructions 118 mayonly include some information necessary to determine and selectalternative electrode combinations because programmer 20 or anotherdevice may perform some or all of the steps in the process.

Stimulation generator 108, under the control of processor 102, generatesstimulation signals for delivery to patient 1 via one or more electrodesdefined by a selected electrode combination. An example range ofelectrical stimulation parameters believed to be effective in DBS tomanage a movement disorder of patient include:

1. Frequency: between approximately 100 Hz and approximately 500 Hz,such as approximately 130 Hz.

2. Voltage Amplitude: between approximately 0.1 volts and approximately50 volts, such as between approximately 1 volts and approximately 10volts, or approximately 3 volts.

3. Current Amplitude: In a current-controlled system, the currentamplitude, assuming a lower level impedance of approximately 500 ohms,may be between approximately 0 milliamps to approximately 100 milliamps,such as between approximately 0.1 milliamps and approximately 40milliamps in some examples. In other examples, the current amplitudesmay be between approximately 0.1 milliamps and approximately 10milliamps, or approximately 3 milliamps in one example. However, in someexamples, the impedance may range between about 200 ohms and about 2kiloohms.

4. Pulse Width: between approximately 10 microseconds and approximately5000 microseconds, such as between approximately 10 microseconds andapproximately 500 microseconds.

Accordingly, in some examples, stimulation generator 108 generateselectrical stimulation signals in accordance with the electricalstimulation parameters noted above. Other ranges of therapy parametervalues may also be useful, and may depend on the target stimulation sitewithin patient 1. While stimulation pulses are described, stimulationsignals may be of any form, such as continuous-time signals (e.g., sinewaves) or the like.

Power monitor 109 may be connected to stimulation generator 108 andinclude circuitry configured to monitor, or measure, power consumptionby one or more current sources of stimulation generator 108. In thismanner, power monitor 109 may provide information to processor 102regarding the power consumption for each alternative electrodecombination or overall set of stimulation parameters used to deliverelectrical stimulation at any given time. Measurement module 111 mayalso be connected to switch module 110 (or a switch matrix) and includecircuitry configured to measure resistance and/or impedance associatedwith each electrode and/or each electrode combination or each loadand/or load combinations connected to stimulation generator 108. Forexample, measurement module 111 may measure resistances of eachelectrode and provide the resistances to processor 102 for generation ofthe R-matrix of all electrodes of lead 60. The R-matrix and/or Z-matrixmay be used to calculate the power consumption that occurs within thetissue of the patient and/or the tissue of the patient and all otherelectrical components between the stimulation generator and the tissue,such that the total power consumption for a system deliveringstimulation therapy would include the power consumption by the tissueand the power consumption that occurs within the system (e.g., withinthe stimulation generator, between the tissue and the stimulationgenerator, and other electrical components).

Processor 102 may control measurement module 111 to measure the R-matrixand/or Z-matrix, or any other representation of tissue resistance and/orload impedance, once or several times over the course of stimulationtherapy. For example, processor 102 may initially control measurementmodule 111 to measure the R-matrix after implantation of lead 60 andprior to selecting stimulation parameters for stimulation therapy. Sincethe composition of tissue around lead 60 and the electrodes thereof maychange over time (e.g., due to encapsulation, scar tissue, etc.),processor 102 may periodically re-measure the R-matrix according to apredetermined schedule and/or in response to detected events. Detectedevents may include a visit by the patient to a clinic, a replacedimplantable component, the loss or failure of an electrode (orcorresponding switch or conductor), or even a traumatic accident enduredby the patient that may have moved the lead relative to tissue. In thismanner, the updated R-matrix may provide for more accurate powerconsumption values and more accurate stimulation field determinationwith associated similarities of alternative electrode combinations orother sets of stimulation parameters.

The R-matrix or Z-matrix, as referred to herein, may describe theresistance, or impedance, of tissue for a specific patient within whichthe electrodes are implanted. It may also describe the load impedance(e.g., electrical components between tissue and stimulation generatorplus the tissue itself) connected to the each current source of thestimulation generator. In this manner, the R-matrix or Z-matrix mayprovide specific information regarding the tissue-electrode interfaceand current path through tissue between electrodes and these electrodesand the stimulation generator. In one example, the R-matrix or Z-matrixmay be calculated applying a test stimulation current between twoelectrodes or between an electrode and a housing of IMD 100, forexample, measuring the resulting excitation voltage, and deriving animpedance between the electrodes based on the test stimulation currentand the resulting excitation voltage. This process may be repeated forall different electrodes, in some examples, or in only some electrodeand extrapolated to other electrodes, in other examples. The teststimulation currents may be at sub-threshold levels (e.g., 0.1 mA) insome examples to avoid neuron activation during impedance measurement,and the resulting measured resistances may be extrapolated up to typicaltherapeutic currents (e.g., 3.0 mA) to provide an R-matrix or Z-matrixrepresentative of actual therapy delivery. In other examples, theR-matrix may be determined using test stimulation currents at normaltherapeutic current levels or using actual therapeutic stimulationduring therapy. Example methods for determining the R-matrix or Z-matrixfor tissue of the patient are described in Patent Cooperation TreatyPublication No. WO 2011/107917 A1 by Emil Toader et al., and entitled“Method and System for Determining Settings for Deep Brain Stimulation,”the entire content of which is incorporated herein by reference.

Processor 102 may include any one or more of a microprocessor, acontroller, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA),discrete logic circuitry, and the functions attributed to processor 102herein may be embodied as firmware, hardware, software or anycombination thereof. Processor 102 controls stimulation generator 108according to therapy programs 116 stored in memory 114 to applyparticular stimulation parameter values specified by one or more ofprograms, such as amplitude, pulse width, and pulse rate.

In the example shown in FIG. 5, the set of electrodes 66, 68, 70, and 72of lead 60 are coupled to switch module 110 for delivery of electricalstimulation. In other examples, two or more leads may be coupled toswitch module 110 with similar or varying configurations of electrodes.Processor 102 also controls switch module 110 to apply the stimulationsignals generated by stimulation generator 108 to selected combinationsof electrodes 66, 68, 70, and 72. In particular, switch module 110 maycouple stimulation signals to selected conductors within lead 60, which,in turn, deliver the stimulation signals across selected electrodes 66,68, 70, and 72. Switch module 110 may be a switch array, switch matrix,multiplexer, or any other type of switching module configured toselectively couple stimulation energy to selected electrodes 66, 68, 70,and 72 and to selectively sense bioelectrical brain signals withselected electrodes 66, 68, 70, and 72. Hence, stimulation generator 108is coupled to electrodes 66, 68, 70, and 72 via switch module 110 andconductors within lead 60. In some examples, however, IMD 100 does notinclude switch module 110.

Stimulation generator 108 may be a single channel or multi-channelstimulation generator. In particular, stimulation generator 108 may becapable of delivering a single stimulation pulse, multiple stimulationpulses, or a continuous signal at a given time via a single electrodecombination or multiple stimulation pulses at a given time via multipleelectrode combinations. In some examples, however, stimulation generator108 and switch module 110 may be configured to deliver multiple channelson a time-interleaved basis. For example, switch module 110 may serve totime divide the output of stimulation generator 108 across differentelectrode combinations at different times to deliver multiple programsor channels of stimulation energy to patient 1.

Although sensing module 106 is incorporated into a common housing withstimulation generator 108 and processor 102 in FIG. 5, in otherexamples, sensing module 106 may be in a separate housing from IMD 100and may communicate with processor 102 via wired or wirelesscommunication techniques. Example bioelectrical brain signals include,but are not limited to, a signal generated from local field potentialswithin one or more regions of the brain. EEG and ECoG signals areexamples of local field potentials that may be measured within thebrain. However, local field potentials may include a broader genus ofelectrical signals within the brain of patient 1.

Sensor 112 may include one or more sensing elements that sense values ofa respective patient parameter. For example, sensor 112 may include oneor more accelerometers, optical sensors, chemical sensors, temperaturesensors, pressure sensors, or any other types of sensors. Sensor 112 mayoutput patient parameter values that may be used as feedback to controldelivery of therapy. IMD 100 may include additional sensors within thehousing of IMD 100 and/or coupled via lead 60 or other leads. Inaddition, IMD 100 may receive sensor signals wirelessly from remotesensors via telemetry module 104, for example. In some examples, one ormore of these remote sensors may be external to patient (e.g., carriedon the external surface of the skin, attached to clothing, or otherwisepositioned external to the patient). Each of the sensor signals may becalibrated by identified patient behavior from video information andincorporated in the feedback control of therapy.

Telemetry module 104 supports wireless communication between IMD 100 andan external programmer 20 or another computing device under the controlof processor 102. Processor 102 of IMD 100 may receive, as updates toprograms, values for various stimulation parameters such as amplitudeand/or alternative electrode combination(s), from programmer 20 viatelemetry module 104. The updates to the therapy programs may be storedwithin therapy programs 116 portion of memory 114. Telemetry module 104in IMD 100, as well as telemetry modules in other devices and systemsdescribed herein, such as programmer 20, may accomplish communication byradiofrequency (RF) communication techniques. In addition, telemetrymodule 104 may communicate with external medical device programmer 20via proximal inductive interaction of IMD 100 with programmer 24.Accordingly, telemetry module 104 may send information to externalprogrammer 24 on a continuous basis, at periodic intervals, or uponrequest from IMD 100 or programmer 24.

Power source 122 delivers operating power to various components of IMD100. Power source 122 may include a small rechargeable battery, anon-rechargeable battery, and/or another type of energy storage devicesuch as one or more super capacitors, and a power generation circuit toproduce the operating power. Recharging may be accomplished throughproximal inductive interaction between an external charger and aninductive charging coil within IMD 100. In some examples, powerrequirements may be small enough to allow IMD 100 to utilize patientmotion and implement a kinetic energy-scavenging device to tricklecharge a rechargeable battery. In other examples, traditional batteriesmay be used for a limited period of time.

FIG. 6 is a functional block diagram of an example external programmer20 for an IMD such as IMD 100 or controller 14. Although programmer 20may generally be described as a hand-held device, programmer 20 may be alarger portable device or a more stationary device. In addition, inother examples, programmer 20 may be included as part of an externalcharging device or include the functionality of an external chargingdevice. As illustrated in FIG. 6, programmer 20 may include a processor130, memory 132, user interface 136, telemetry module 137, and powersource 138. Memory 132 may store instructions that, when executed byprocessor 130, cause processor 130 and external programmer 20 to providethe functionality ascribed to external programmer 20 throughout thisdisclosure. For example, configuration instructions 134 in memory 132may cause programmer 20 to determine alternative electrode combinationsand receive user input selecting an alternative electrode combination toreduce power consumption of stimulation therapy.

In general, programmer 20 comprises any suitable arrangement ofhardware, alone or in combination with software and/or firmware, toperform the techniques attributed to programmer 20, and processor 130,user interface 136, and telemetry module 137 of programmer 20. Invarious examples, programmer 20 may include one or more processors, suchas one or more microprocessors, DSPs, ASICs, FPGAs, or any otherequivalent integrated or discrete logic circuitry, as well as anycombinations of such components. Programmer 20 also, in variousexamples, may include a memory 132, such as RAM, ROM, PROM, EPROM,EEPROM, flash memory, a hard disk, a CD-ROM, comprising executableinstructions for causing the one or more processors to perform theactions attributed to them. Moreover, although processor 130 andtelemetry module 137 are described as separate modules, in someexamples, processor 130 and telemetry module 137 are functionallyintegrated. In some examples, processor 130 and telemetry module 137correspond to individual hardware units, such as ASICs, DSPs, FPGAs, orother hardware units.

Memory 132 (e.g., a storage device) may store instructions that, whenexecuted by processor 130, cause processor 130 and programmer 20 toprovide the functionality ascribed to programmer 20 throughout thisdisclosure. For example memory 132 may include instructions that causeprocessor 130 to obtain a parameter set from memory, select a spatialelectrode movement pattern, or receive a user input and send acorresponding command to IMD 14, or instructions for any otherfunctionality. In addition, memory 132 may include a plurality oftherapy programs 133 (similar to therapy programs 116 of FIG. 5), whereeach therapy program includes a parameter set that defines stimulationtherapy.

Configuration instructions 134 may be similar to configurationinstructions 118 of IMD 100 and may include rules, algorithms, data, orany other information related to determining alternative electrodecombinations, calculating power consumption values and stimulation fieldsimilarity scores, and selecting an alternative electrode combinationfor therapy. For example, configuration instructions 134 may include oneor more algorithms defining how to generate different alternativeelectrode combinations based on an initial electrode combination.Configuration instructions 134 may also include instructions regardingwhether processor 130 should automatically select an alternativeelectrode combination or present alternative electrode combinations to auser for selection. For example, configuration instructions 134 maydefine how power consumption values, field similarity scores, and/orvisual representations of stimulation fields are determined orcalculated and/or generated for presentation to a user. In someexamples, configuration instructions 134 may only include someinformation necessary to determine and select alternative electrodecombinations because programmer 20 or another device may perform some orall of the steps in the process.

User interface 136 may include a button or keypad, lights, a speaker forvoice commands, a display, such as a liquid crystal (LCD),light-emitting diode (LED), or organic light-emitting diode (OLED). Insome examples the display may be a touch screen. User interface 136 maybe configured to display any information related to the delivery ofstimulation therapy, alternative electrode combinations, or any othersuch information. User interface 136 may also receive user input viauser interface 136. The input may be, for example, in the form ofpressing a button on a keypad or selecting an icon from a touch screen.

Telemetry module 137 may support wireless communication betweencontroller 114 or IMD 14 and programmer 20 under the control ofprocessor 130. Telemetry module 137 may also be configured tocommunicate with another computing device via wireless communicationtechniques, or direct communication through a wired connection. In someexamples, telemetry module 137 may be substantially similar to telemetrymodule 104 of IMD 100 described herein, providing wireless communicationvia an RF or proximal inductive medium. In some examples, telemetrymodule 137 may include an antenna, which may take on a variety of forms,such as an internal or external antenna.

Examples of local wireless communication techniques that may be employedto facilitate communication between programmer 20 and controller 14 orIMD 100 include RF communication according to the 802.11 or Bluetoothspecification sets or other standard or proprietary telemetry protocols.In this manner, other external devices may be capable of communicatingwith programmer 20 without needing to establish a secure wirelessconnection. As described herein, telemetry module 137 may be configuredto transmit a spatial electrode movement pattern or other stimulationparameter values to controller 14 or IMD 100 for delivery of stimulationtherapy.

FIG. 7 is a conceptual diagram of an example distributed system 140 thatoperates over a network. As shown in FIG. 7, system 140 that includesnetworked server 146 coupled to IMD 14 (and/or controller 14) and one ormore computing devices 150 via network 142. Server 146 (e.g., anetworked external computing device) and one or more computing devices150A-150N that are coupled to the IMD 14 and programmer 20 via a network142. Network 142 may be generally used to transmit sensed data and/orinformation related to determining and/or selecting alternativeelectrode combinations. For example, programmer 20 may send alternativeelectrode combinations and the initial electrode combination to sever146 in order for server 146 to calculate data such as power consumptionvalues, field similarity scores, and/or 2D or 3D graphicalrepresentations of the stimulation fields. Such information may becomputationally intensive and benefit from offloading from programmer 20and or IMD 14. The distributed computing of system 140 may be used forany process described herein.

In some examples, the information transmitted by IMD 14 may allow aclinician or other healthcare professional to monitor patient 1remotely. In some examples, IMD 14 may use a telemetry module tocommunicate with programmer 20 via a first wireless connection, and tocommunicate with access point 144 via a second wireless connection,e.g., at different times. In the example of FIG. 7, access point 144,programmer 20, server 146 and computing devices 150A-150N areinterconnected, and able to communicate with each other through network142. In some cases, one or more of access point 144, programmer 20,server 146 and computing devices 150A-150N may be coupled to network 142via one or more wireless connections. IMD 14, programmer 20, server 146,and computing devices 150A-150N may each comprise one or moreprocessors, such as one or more microprocessors, DSPs, ASICs, FPGAs,programmable logic circuitry, or the like, that may perform variousfunctions and operations, such as those described herein.

Access point 144 may comprise a device that connects to network 142 viaany of a variety of connections, such as telephone dial-up, digitalsubscriber line (DSL), or cable modem connections. In other examples,access point 144 may be coupled to network 142 through different formsof connections, including wired or wireless connections. In someexamples, access point 144 may be co-located with patient 14 and maycomprise one or more programming units and/or computing devices (e.g.,one or more monitoring units) that may perform various functions andoperations described herein. For example, access point 144 may include ahome-monitoring unit that is co-located with patient 14 and that maymonitor the activity of IMD 14. In some examples, server 146 orcomputing devices 150 may control or perform any of the variousfunctions or operations described herein.

In some cases, server 146 may be configured to provide a secure storagesite for archival of video information, therapy parameters, patientparameters, or other data that has been collected and generated from IMD14 and/or programmer 20. Network 142 may comprise a local area network,wide area network, or global network, such as the Internet. The systemof FIG. 7 may be implemented, in some aspects, with general networktechnology and functionality similar to that provide by the MedtronicCareLink® Network developed by Medtronic, Inc., of Minneapolis, Minn.

FIG. 8 is a conceptual diagram of example alternative electrodecombinations selected based on the distance of other electrodes to anelectrode of the initial electrode combination. As shown in FIG. 8,electrodes 160 is a set of 18 electrodes in a staggered configurationsuch as electrodes 28 of FIG. 2A. Alternative electrode combinations maybe based on an initial electrode combination and the distance from anelectrode of an initial electrode combination to adjacent electrodes.

In one example, programmer 20, for example, may start with an initialelectrode combination and add electrodes to generate alternativeelectrode combinations. In one example, the distances may be theEuclidian distance based on an “unwrapping” or “unrolling” of thecomplex electrode array geometry as shown in FIG. 8. Electrode A may bethe single electrode of the initial electrode combination. Adjacent toelectrode A are four electrodes B that are each the same distance 162from electrode A. Programmer 20 may thus define a first alternativeelectrode combination as electrodes A and B (e.g., 5 electrodes). At thenext distance 164 that is further from electrode A, programmer 20 mayadd electrodes C to determine the second alternative electrodecombination as electrodes A, B, and C (e.g., 9 electrodes). At the nextdistance 166 that is again further from electrode A, programmer 20 mayadd electrodes D to determine the third alternative electrodecombination as electrodes A, B, C, and D (e.g., 13 electrodes). Byiteratively adding electrodes at further distances from electrode A,programmer 20 may have determined some electrode combinations with lowerimpedances and/or power consumption values than just electrode A.

In the example of FIG. 8, the distances 162, 164, and 166 are calculatedfrom the center of electrode A to the center of the other respectiveelectrodes. However, in other examples, the distance between electrodesmay be calculated from the middle of the initial electrode to thenearest edge of another electrode, from the nearest edges between twoelectrodes, or according to any other algorithm. Distances 162, 164, and166 are calculated as Euclidian distances. Other methods for determiningdistances may be used in other examples. For example, on a cylindricallead, programmer 20 may calculate the arc distance around the surface ofthe lead from one electrode to another electrode. In other examples,programmer 20 may model the expected average path of electrical currentthrough tissue from the initial electrode to alternative electrodes. Inother words, the electrical path may arc at some distance away from thesurface of the lead. Programmer 20 may use the expected average path ofthe electrical current as the distance between two electrodes.

As shown in the example of FIG. 8, all electrodes at each equidistantlocation from electrode A may be used in order to maintain the symmetryof the stimulation field to the stimulation field of the initialelectrode combination. Programmer 20 may continue to determineadditional alternative electrode combinations if further electrodes ofthe complex electrode array geometry are available or until asymmetrical group of electrodes can no longer be added. However,additional electrodes will continue to alter the stimulation field. Inother examples, electrodes added for a single alternative electrodecombination may not all be at exactly equidistant from the initialelectrode. Instead, programmer 20 may use two or more electrodes withina range of distances of the initial electrode. Using a distance rangemay be appropriate for electrode arrays that are unsymmetrical or havevaried distances between adjacent electrodes. Such a range may also beuseful when the initial electrode combination includes two or moreelectrodes.

The example of FIG. 8 illustrates an initial electrode combination ofone electrode. However, the initial electrode combination may includetwo or more electrodes. For multiple electrodes in the initial electrodecombination, subsequent alternative electrode combinations may bedetermined by adding the next closest available electrodes. The newalternative electrode combinations may add electrodes to generallymaintain the original spatial shape of the initial electrode combinationor otherwise attempt to maintain the stimulation field shape. In otherexamples, programmer 20 may determine one or more alternative electrodecombinations by shifting one or more electrodes in one direction fromthe initial electrode combination. In this manner, alternative electrodecombinations may be determined via asymmetrical shifting of electrodes,addition of electrodes, or even subtraction of electrodes. Alternativeelectrode combinations may include fewer electrodes than an initialelectrode combination if the electrodes of the alternative electrodecombination have a lower collective impedance than the electrodes of theinitial electrode combination. This may occur based on differences intissue resistance surrounding the electrodes of the lead, for example.

Electrodes 160 are shown as staggered levels of electrodes. However,different electrode arrays may have different configurations ofelectrodes. For example, electrodes 160 may be shown in aligned rows andcolumns that represent lead 60 of FIG. 4. Any type of electrodeconfiguration may be shown in such a manner.

In some examples, programmer 20 may continue to generate alternativeelectrode combinations until the field similarity score drops below apredetermined threshold. For example, programmer 20 may calculate afield similarity score for a newly determined alternative electrodecombination with respect to the initial electrode combination. If thefield similarity score is below a threshold of 80%, for example,programmer 20 may stop generating any additional alternative electrodecombinations because further additions of electrodes will likely furtherdecrease the field similarity score. Programmer 20 may or may notdiscard any alternative electrode combinations that have a fieldsimilarity score below the predetermined threshold. The predeterminedthreshold may be set to any desired threshold, such as about 50%, 60%,70%, 80%, or 90%, or any other threshold lower, higher, or in betweenthese thresholds. In some examples, the predetermined threshold for thefield similarity score may be used as one input for determining how manyalternative electrode combination are generated. Programmer 20 may, forexample, generate at least a predetermined number of alternativeelectrode combinations even if one or more of the alternative electrodecombinations have a field similarity score below the predeterminedthreshold. In other examples, programmer 20 may only generate thepredetermined number of alternative electrode combinations (e.g., two,three, four, five, or more) even if the field similarity scores arestill above the predetermined threshold.

When calculating and/or measuring the power consumption values and/orstimulation fields for the initial electrode combination and thealternative electrode combinations, programmer 20 may assume the samestimulation parameters (e.g., current or voltage amplitude, pulse width,pulse frequency, etc.) for each of the electrodes across all electrodecombinations. In the alternative, programmer 20 may use one or moredifferent stimulation parameters between different alternative electrodecombinations or even one or more different stimulation parameters fordifferent electrodes within the same alternative electrode combination.For example, more centrally located electrodes of an alternativeelectrode combination may use higher current or voltage amplitudes thanmore peripheral electrodes. In other examples, peripheral electrodes ofthe alternative electrode combinations may have higher current orvoltage amplitudes than more centrally located electrodes of theelectrode combination. These different stimulation parameter values mayallow for further reduction in power consumption and/or more similarstimulation fields when compared to the initial electrode combinations.

In some examples, programmer 20 may assume that all electrodes 160 ofthe complex electrode array are available for stimulation and inclusionin alternative electrode combinations. However, one or more electrodesmay not function as intended due to conductor fracture between anelectrode and the stimulation generator, switch matrix error or failure,or even excessive encapsulation that raises the impedance of anelectrode. Controller 14 or IMD 100 may periodically test each electrodeand determine whether or not each electrode is still functional oravailable to deliver stimulation therapy. This periodic testing mayinclude re-determining, re-measuring or re-calculating the electroderesistance (e.g., R-matrix) or impedance (e.g., Z-matrix) for allelectrodes, electronics, and tissue associated with the system.Programmer 20 may use the results of the test (or resistance/impedancematrix) when determining alternative electrode combinations. Goodelectrodes may be available, or alternatively, bad electrodes may berestricted from being used in an electrode combination. Therefore, whendetermining alternative electrode combinations, programmer 20 may onlyuse functioning electrodes for each alternative electrode combination.

The example of FIG. 8 may be used when the initial electrode combinationand alternative electrode combinations are used in a monopolar orunipolar configuration. In a monopolar or unipolar configuration, one ormore ground electrodes may be located on controller 14 of IMD 100 (e.g.,carried on the implant housing), on a portion of the lead or connectionbetween the IMD and the lead, or as part of second module 17. In otherexamples, one or more electrodes (e.g., one or more levels of a complexelectrode array geometry) that are not selected as active electrodes maybe utilized as a ground electrode that sinks current that is sourcedfrom the active electrodes. In other examples, bipolar configurations ofelectrodes may be used. In a bipolar configuration, alternativeelectrode combinations may be determined for one or more of the initialanode and/or cathode electrodes of the initial electrode combination.

As described herein, programmer 20 may calculate various metrics tocharacterize the alternative electrode combinations. Programmer 20 maycalculate a power consumption value and a field similarity score foreach of the alternative electrode combinations. Table 1 provided belowprovides information for each of the initial (or original) electrodecombination and the determined alternative electrode combinations. Forexample, Table 1 includes the Euclidian distance, Power consumption,Power consumption reduction percentage, and Sorensen-Dice fieldsimilarity score for each electrode combination. Both of the powerconsumption and power consumption reduction percentage may be referredto as a power consumption reduction value.

TABLE 1 Power Power Electrode Euclidean consumption consumptionSørensen- configuration distance [units] [mW] Reduction Dice Original0.0 12.5 0% 100% (1 contact) Configuration 1 1.4 3.8 70% 93% (5contacts) Configuration 2 2.0 2.7 78% 88% (9 contacts) Configuration 32.8 2.1 83% 81% (13 contacts)

In the example of Table 1 and FIG. 8, the “Original” electrodecombination corresponds to electrode A, “Configuration 1” corresponds toelectrodes A and B, “Configuration 2” corresponds to electrodes A, B,and C, and “Configuration 3” corresponds to electrodes A, B, C, and D.The Euclidian distance represents the distances 162, 164, and 166,respectively. The Power consumption may be the absolute powerconsumption based on the common current (e.g., 1.5 mA) and the totalimpedance of the electrodes in each electrode combination, and theimpedance of the remainder of the system (which may include additionalelectronics and/or tissue impedances associated with each electrode).The Power consumption reduction percentage may be the percentagedecrease of the total power consumption for the alternative electrodecombination as compared to the initial electrode combination. TheSorensen-Dice field similarity score may be the numerical valueattributed to the similarity of the stimulation field from thealternative electrode combination to the stimulation field from theinitial electrode combination.

The information in Table 1 may be output and presented to a user as arepresentation of the alternative electrode combination. A user mayreview the information of Table 1 and base the selection of one of thealternative electrode combination on the data of Table 1. If programmer20, controller 14, IMD 100, or any other device automatically selects analternative electrode combination for stimulation therapy, programmer 20may still present the information for the selected alternative electrodecombination or even all of the possible alternative electrodecombinations for the user to review. Programmer 20 may require the userto confirm the automated selection of the alternative electrodecombination, or programmer 20 may present a mechanism for the user toreject the selected alternative electrode combination and receive userselection for a different alternative electrode combination or even theinitial electrode combination if none of the alternative electrodecombinations are acceptable to the user.

The alternative electrode combinations may be ranked in Table 1according to a variety of factors. In one example, the alternativeelectrode combination may be ranked according to decreasing fieldsimilarity scores. In other examples, the alternative electrodecombinations may be ranked based in decreasing power consumption values,increasing number of electrodes, or any other variations. In someexamples, alternative electrode combinations may be displayed withinformation regarding patient feedback for the various alternativeelectrode combinations if the combination has been used and reviewed bythe patient. In this manner, programmer 20 may display feedback scoresfrom the patient that may or may not correspond to the calculated fieldsimilarity score.

FIG. 9 is a conceptual diagram of example stimulation fields deliverablefrom alternative electrode combinations. As shown in FIG. 9, programmer20 (or any other device described herein) has generated and presentedgraphical representations of the stimulation fields deliverable by eachof the initial electrode combination and the alternative electrodecombinations discussed in FIG. 8. Representation 170 may be arepresentation of the stimulation fields that can be output anddisplayed to a user via programmer 20, for example. Axial views 172include the axial views of each of stimulation fields 180A, 180B, 180C,and 180D (collectively “stimulation fields 180”) with respect to lead176. With respect to the electrode combinations of FIG. 8, stimulationfield 180A corresponds to the initial electrode configuration ofelectrode A, stimulation field 180B corresponds to the alternativeelectrode configuration of electrodes A and B, stimulation field 180Ccorresponds to the alternative electrode configuration of electrodes A,B, and C, and stimulation field 180D corresponds to the alternativeelectrode configuration of electrodes A, B, C, and D.

Field width scale 178 includes multiple dotted lines that indicate thedistance the stimulation field reaches out from lead 176. Field widthscale 178 is provided with each of stimulation fields 180 in order toreview the relative sizes of each stimulation field. For example, fieldwidth scale 178 shows that stimulation field 180A provides a widerstimulation field than stimulation field 180D. Each dotted line of fieldwidth scale 178 may correspond to a respective distance from lead 176 ina scale of millimeters, centimeters, inches, or any other distancescale.

Side views 174 include side views of each of stimulation fields 180A,180B, 180C, and 180D with respect to the side view of lead 176. As shownin side views 174, as more electrodes are used to generate thestimulation fields 180A-180D, the length of the stimulation fieldincreases in size. In other words, stimulation field 180A from oneelectrode provides a shorter stimulation field along the length of lead174 than stimulation field 180D provided by 13 electrodes. Although notshown in FIG. 9, a field height scale (such as field width scale 178)may also be shown in conjunction with the side views of stimulationfields in side views 174.

Axial views 172 and side views 174 may be referred to as 2Drepresentations of the stimulation fields. In some examples, programmer20 may allow a user to rotate each stimulation field 180 as desired. Inother examples, one or more 3D representation of each stimulation fieldmay be displayed. Programmer 20 may receive user input that rotates,spins, or moves the stimulation field in three dimensions in order toview the stimulation field. In some examples, stimulation fields 180,and possibly lead 176, may be shown in conjunction with a representationof patient anatomy. Programmer 20 may thus display stimulation fields180 over anatomical structures so that the user can view whether or notstimulation fields 180 stimulate desired anatomical regions and/orundesirable anatomical regions.

In some examples, programmer 20 may generate and display stimulationfields 180 as different colors. The different colors may be used to keyeach stimulation field to a respective electrode combination. In otherexamples, different colors or patterns of stimulation fields 180 mayindicate a comparison to the initial electrode combination. For example,different colors of stimulation fields 180 may be indicative of thepower consumption value. Green color shades may indicate less powerconsumption and red color shades may indicate more power consumption,for example. In other examples, a color or pattern of stimulation fields180 may indicate how similar the stimulation field is to the initialelectrode combination. In this manner, representation 170 may providemore information about the alternative electrode combinations thanmerely a graphic representation of the stimulation fields.

FIG. 10 is a flow diagram of an example process for determiningalternative electrode combinations according to the present disclosure.The process of FIG. 10 will be described with regard to processor 130 ofprogrammer 20. However, this process, or portions of the process, may beperformed by other devices such as controller 14, IMD 100, networkedserver 146, or computing devices 150. In this manner, one device, orseveral networked devices, may perform the process of FIG. 10.

As shown in FIG. 10, processor 130 identifies a first electrodecombination (e.g., set of one or more electrodes or an initial electrodecombination) (200). Processor 130 may identify the first electrodecombination by receiving user input that defines the first electrodecombination or from another therapy programmer. In other examplesprocessor 130 may identify the first electrode combination from aselected stimulation program, one or more electrodes determined asavailable for stimulation from a user, or as corresponding to a user orsystem desired anatomical region or direction with respect to the lead.If processor 130 determines that there is an alternative electrodecombination available (“YES” branch of block 202), processor 130 maydetermine the new alternative electrode combination (204). Processor 130may determine the new alternative electrode combination by addingadditional electrodes to the electrodes of the initial electrodecombination or the previously generated alterative electrodecombination.

If processor 130 determines that there are no more alterative electrodecombinations available (“NO” branch of block 202), processor 130 maythen determine (e.g., calculate or measure) power consumption values foreach of the alterative electrode combinations (206). Processor 130 alsocalculates stimulation fields for each of the alterative electrodecombinations (208). Using the calculated stimulation fields, processor130 also determines the similarity of the stimulation field of eachalternative electrode combination to the stimulation field of the firstelectrode combination (210). For example, processor 130 may calculate afield similarity score such as a Sorensen-Dice coefficient.

Once processor 130 has determined attributes for each of the alterativeelectrode combinations, processor 130 may output, for display, arepresentation of the power consumption values and stimulation fieldsimilarity values for one or more of the alterative electrodecombinations (212). For example, processor 130 may control userinterface 136 to display the information of Table 1 and/or thestimulation fields of representation 170 of FIG. 9. Via user interface136, processor 130 receives user selection of one of the alterativeelectrode combination for stimulation therapy (214). Processor 130 thencontrols an IMD (e.g., controller 14 or IMD 100) to deliver stimulationtherapy according to the selected alternative electrode combination(216). In other examples, as described herein, processor 130 mayautomatically select one of the alterative electrode combinations.Processor 130 may request user confirmation of the selected alterativeelectrode combination and/or present information about the selectedalterative electrode combination.

Processor 130 may initiate the process of FIG. 10 in a variety ofsituations. Processor 130 may propose alterative electrode combinationsany time that processor 130 receives a user defined electrodecombination intended for stimulation therapy. In other examples,processor 130 may propose alterative electrode combinations when atherapy program is first selected to be used for stimulation therapy.Alternatively, processor 130 may propose alterative electrodecombination in response to detecting inadequate battery life or someother unexpected or undesirable power usage of the IMD. Processor 130may thus propose alterative electrode combinations in order to extendbattery life of the system or otherwise improve the amount of time forwhich the IMD can deliver stimulation therapy between rechargingintervals.

The process of FIG. 10 is directed to determining alternative electrodecombinations using the same or similar stimulation parameters such aspulse width, current or voltage amplitude, pulse frequency, etc.However, processor 130 may perform an alternative process for FIG. 10 inwhich different sets of stimulation parameters, not just differentelectrode combinations, are determined. These different sets ofstimulation parameters may include alternatives to one or more of thepulse frequency, pulse width, duty cycle, current or voltage amplitude,or any other stimulation parameter. For each of these alternative setsof stimulation parameters determined by processor 130, processor 130 maydetermine respective power consumption values and stimulation fieldsimilarity values. Processor 130 may then use an alternative set ofstimulation parameters to control delivery of stimulation therapy to thepatient. A process of selecting different sets of stimulation parametersmay require one or more constraints that limit the system to certainranges of values such as minimum or maximums for number of electrodes,current or voltage amplitude, pulse width, pulse frequency, etc.

FIG. 11 is a conceptual diagram illustrating an example monopolarstimulation circuit that represents elements of the system that maycontribute to the impedance of one or more electrodes for each of arespective current source. Circuit 220 may be representative of astimulation circuit associated with system 10, for example. Circuit 220may represent various sources of current, capacitance, and resistancethat contributes to the overall impedance of the system for any givenelectrode or electrode combination. As shown in FIG. 11, circuit 220includes stimulator block 222 representing elements of controller 14 orIMD 100 (which may include two push-pull current sources 230A and 230Bas shown, one push-pull current source, or three or more push-pullcurrent sources), lead cable block 224 representing elements ofconnecting cable 16, second module block 226 representing elements ofsecond module 17, lead block 228 representing elements of lead 22 andelectrodes thereof, and tissue block 230 representing the resistance oftissue between the electrodes and ground terminal 246. These componentsof circuit 220 may represent or model one or more electrical componentsthat may contribute to the overall system impedance and powerdissipation of the circuit. Although circuit 220 may represent actualelectrical components present in the system in some examples, circuit220 may be a general approximation of the electrical characteristics ofone or more electrical components of a stimulation circuit for modelingpurposes.

When measuring, calculating, or otherwise determining the impedance orresistance of the circuit for an electrode combination, variouscomponents of the entire system, including the tissue through which theelectrical signal propagates, may be considered. Sub-circuit 221A mayinclude those components used to provide stimulation from current source230A and sub-circuit 221B includes those components used to providestimulation from push-pull current source 230B. In the example ofsub-circuit 221A, contributors to the overall impedance (or alsoreferred to as a collective impedance for an electrode combination) oroverall load of push-pull current source 230A may include blockingcapacitor 232A of stimulator block 222 and resistance 234A of one ormore conductors of lead block 228. Additional contributors to the loadimpedance of push-pull current source 230A of sub-circuit 221A mayinclude components of second module block 226 such as one or moreblocking capacitors 236A, resistors 238A and 238B of a switch matrix,blocking capacitors 240A and 240B, components of lead block 228 such aslead resistors 242A and 242B (e.g., conductive traces or conductors) andcorresponding capacitors 244A and 244B representing the respectiveelectrodes (e.g., the interface between electrodes and adjacent tissue),and impedance of tissue block 230 before the electrical current reachesground terminal 246 (e.g., the housing of controller 14 or a returnelectrode). In some examples, tissue block 230 may represent theR-matrix, or resistance matrix, or Z-matrix, or impedance matrix, of theelectrodes of the lead. The R-matrix and Z-matrix may be described asthe brain tissue spreading resistance or impedance, respectively, insome examples and be used as a representation of the tissue resistanceor impedance that corresponds to each electrode. In some examples, theR-matrix or Z-matrix may be measured via test pulses or other excitationwaveforms (e.g., square wave currents, voltages, etc.) generated fromthe stimulation generator (e.g., one or more current sources) orseparate measurement module (e.g., a measurement module 111 of FIG. 5that includes both an excitation source and measurement circuitry tomeasure the response to the excitation pulse(s) that allows measurementof the R-matrix or Z-matrix). Sub-circuit 221A is representative of twoelectrodes being driven, but any number of electrodes may be representedby respective components such as resistance 238A, capacitor 240A,resistor 242A, and capacitor 244A.

Impedances for sub-circuit 221B may be similar to the components ofsub-circuit 221A. For example, sub-circuit 221B may include push-pullcurrent source 230B, blocking capacitor 232B, resistor 234B, blockingcapacitor 236B, resistors 238C and 238D, capacitors 240C and 240D,resistors 242C and 242D, and capacitors 244C and 244D. Each of thecomponents of sub-circuits 221A and 221B represent one or more of thosecomponents, so the illustration of only one component is to simplify thediscussion of possible elements that contribute to the system and/orload impedance. In other examples, additional or fewer sources ofcapacitance and/or resistance may be present in the system. For example,blocking capacitors 236A and 240A and resistor 238A, 238B, 242A and 242Bmay not be present in IMD 100 that includes the simulation generator 108(e.g., one or more current sources) and switch module 110. Circuit 220represents a monopolar stimulation configuration. However, similarcircuits can be used to model or represent components that contribute toimpedances for bipolar stimulation configurations. Other models can beused to represent components that contribute to impedances formulti-implant set-ups.

Power consumption values calculated or measured for each respectivesub-circuit 221A and 221B may incorporate the effects of currentinjected to tissue block 230 by the other sub-circuit in multiplecurrent source examples. For example, current (e.g., I_(PG1)) frompush-pull current source 230A applied to tissue block 230, which has aresistance, which can be represented by the R-matrix or Z-matrix,creates a voltage potential on the electrodes and components ofsub-circuit 221B because the same tissue is in electrical contact withall electrodes of both sub-circuits 221A and 221B. In this manner,presence of a current from sub-circuit 221A causes a change of thevoltage potential at push-pull current source 230B of sub-circuit 221Bwhich may require a change in the supply rail voltages HV+,2 and/orHV−,2 of push-pull current source 230B in order to keep driving theelectrode combination of sub-circuit 221B with the desired current. Thischange in supply rail voltage(s) may also increase the power drawn bypush-pull current source 230B from these rails. This phenomenon may berepresented by using the R-matrix or Z-matrix described herein and isfurther discussed with respect to FIG. 12.

FIG. 12 is a conceptual diagram illustrating an example load model formultiple stimulation generators in a system. Load model 250 mayrepresent circuits similar to sub-circuits 221A and 221B of FIG. 11 andillustrate the coupling that can occur between electrodes of thedifferent sub-circuits each having its own current source. Load model250 includes stimulator blocks 222A and 222B which include therespective current sources and blocking capacitors for sub-circuits 221Aand 221B of FIG. 11. Each stimulator block 222A and 222B can inject acurrent, I₁ and I₂, respectively, into the stimulation load 253represented by the large dotted-line box. Capacitors 251A and 251Brepresent capacitances in the respective circuit due to blockingcapacitors, for example, and resistors 252A and 252B representresistances in the respective circuit due to switches, conductors, etc.Capacitors 254A and 254B represent the capacitances of theelectrode-tissue interface of the electrode combinations for eachcircuit.

Characteristics of tissue 266 are represented by the small dotted-linebox. Tissue 266 may be a more detailed model of tissue block 230 in FIG.11. The elements within tissue 266 represent the elements of theR-matrix or Z-matrix as discussed herein. For example, resistor 256Arepresents the resistance of tissue associated with the electrodecombination driven by current from stimulation block 222A and resistor256B represents the resistance of tissue associated with the electrodecombination driven by current from stimulation block 222B. Resistor 260may represent the bulk resistance of the tissue far from the electrodes(which may be relatively small), and capacitor 262 may represent thecapacitance of the controller housing when used as the grounded (264)return electrode in this example monopolar stimulation load model. Ifeach of stimulation block 222A and 222B, and their respective circuitelements, operated independently or into electrically isolated tissue,the load for each respective current source would not affect the load tothe other current source.

However, this is not the case when multiple current sources areproviding current to the same electrically coupled tissue 266. Currentprovided by one current source instead creates a voltage potentialacross the components of the other circuit because all electrodes areelectrically coupled by the same conductive tissue in which they reside(e.g., brain tissue). Controlled voltage source 258A represents thechange in voltage stimulation block 222A experiences due to the currentinjected by stimulation block 222B, while controlled voltage source 258Brepresent the change in voltage stimulation block 222B experiences dueto the current injected by stimulation block 222A. The voltage of eachcontrolled source 256A and 256B may be calculated by the product of thetransresistance (R_(x)) for the electrode combinations connected tostimulation block 222A and 222B and the current (I₁ or I₂) injected intothe tissue by the other circuit. V_(1,e) and V_(2,e) represents thevoltages developed across the spreading resistance for each electrodecombination for each circuit (which may be the main contributor totissue resistance). In this manner, the known or measured R-matrix orZ-matrix can be used to establish this relationship and determine thearising voltages and currents for the tissue 266. A simplerepresentation of the resistance matrix is provided below in equation 2:

$\begin{matrix}{{\begin{pmatrix}V_{1,e} \\V_{2,e}\end{pmatrix} = {\begin{pmatrix}R_{11} & R_{x} \\R_{x} & R_{22}\end{pmatrix}\begin{pmatrix}I_{1} \\I_{2}\end{pmatrix}}},} & (2)\end{matrix}$where V_(1,e) and V_(2,e) are the voltages developed across thespreading resistance of each electrode combination of each sub-circuit,R11 is the resistance of resistor 256A, R22 is the resistance ofresistor 256B, and R_(x) is the transresistance of the tissue. A largermatrix may be used to represent each electrode, or electrodecombination, in some examples, while a larger matrix may be used torepresent more than two stimulation blocks. If a full matrix is derivedfor all electrodes of a lead (e.g., a 40×40 matrix for 40 electrodes ofa lead), then the system may derive all other resistance or impedancematrices for any other smaller matrices such as the example 2×2 R-matrixdescribed above. The R-matrix above may be determined by measuring theresponse to test stimulation pulses applied to the tissue for theselected electrode combinations and then used to calculate or otherwisedetermine the power consumption values for these selected electrodecombinations that may or may not be affected by current delivered viaanother electrode combination and corresponding current source. Althoughthe R-matrix is shown, the Z-matrix, or impedance matrix, may also becalculated be incorporating reactances of the tissue, for example,capacitive coupling between sets of electrode combinations. Programmer20, or any other device herein, may use the R-matrix or Z-matrixdescribed herein to calculate or determine power consumption values forcertain stimulation parameters, including electrode combinations, whenmultiple current sources may be present in the overall system.

While techniques described herein are discussed primarily in regards toDBS therapy, one or more such techniques may be applied to treatdisorders such as chronic pain disorders, urinary or fecal incontinence,sexual dysfunction, obesity, gastroparesis, and may involve other typesof stimulation such as spinal cord stimulation, cardiac stimulation,pelvic floor stimulation, sacral nerve stimulation, peripheral nervestimulation, peripheral nerve field stimulation, gastric stimulation, orany other electrical stimulation therapy.

In addition, it should be noted that system 10 may not be limited totreatment or monitoring of a human patient. In alternative examples,system 10 may be implemented in non-human patients, e.g., primates,canines, equines, pigs, and felines. These other animals may undergoclinical or research therapies that my benefit from the subject matterof this disclosure.

The techniques of this disclosure may be implemented in a wide varietyof computing devices, medical devices, or any combination thereof. Anyof the described units, modules or components may be implementedtogether or separately as discrete but interoperable logic devices.Depiction of different features as modules or units is intended tohighlight different functional aspects and does not necessarily implythat such modules or units must be realized by separate hardware orsoftware components. Rather, functionality associated with one or moremodules or units may be performed by separate hardware or softwarecomponents, or integrated within common or separate hardware or softwarecomponents.

The disclosure contemplates computer-readable storage media comprisinginstructions to cause a processor to perform any of the functions andtechniques described herein. The computer-readable storage media maytake the example form of any volatile, non-volatile, magnetic, optical,or electrical media, such as a RAM, ROM, NVRAM, EEPROM, or flash memorythat is tangible. The computer-readable storage media may be referred toas non-transitory. A server, client computing device, or any othercomputing device may also contain a more portable removable memory typeto enable easy data transfer or offline data analysis.

The techniques described in this disclosure, including those attributedto various modules and devices (e.g., controller 14, second module 17,IMD 100, or programmer 20) and various constituent components, may beimplemented, at least in part, in hardware, software, firmware or anycombination thereof. For example, various aspects of the techniques maybe implemented within one or more processors, including one or moremicroprocessors, DSPs, ASICs, FPGAs, or any other equivalent integratedor discrete logic circuitry, as well as any combinations of suchcomponents, remote servers, remote client devices, or other devices. Theterm “processor” or “processing circuitry” may generally refer to any ofthe foregoing logic circuitry, alone or in combination with other logiccircuitry, or any other equivalent circuitry.

Such hardware, software, firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. In addition, any of thedescribed units, modules or components may be implemented together orseparately as discrete but interoperable logic devices. Depiction ofdifferent features as modules or units is intended to highlightdifferent functional aspects and does not necessarily imply that suchmodules or units must be realized by separate hardware or softwarecomponents. Rather, functionality associated with one or more modules orunits may be performed by separate hardware or software components, orintegrated within common or separate hardware or software components.

The techniques described in this disclosure may also be embodied orencoded in an article of manufacture including a computer-readablestorage medium encoded with instructions. Instructions embedded orencoded in an article of manufacture including a computer-readablestorage medium, may cause one or more programmable processors, or otherprocessors, to implement one or more of the techniques described herein,such as when instructions included or encoded in the computer-readablestorage medium are executed by the one or more processors. Examplecomputer-readable storage media may include random access memory (RAM),read only memory (ROM), programmable read only memory (PROM), erasableprogrammable read only memory (EPROM), electronically erasableprogrammable read only memory (EEPROM), flash memory, a hard disk, acompact disc ROM (CD-ROM), a floppy disk, a cassette, magnetic media,optical media, or any other computer readable storage devices ortangible computer readable media. The computer-readable storage mediummay also be referred to as storage devices.

In some examples, a computer-readable storage medium comprisesnon-transitory medium. The term “non-transitory” may indicate that thestorage medium is not embodied in a carrier wave or a propagated signal.In certain examples, a non-transitory storage medium may store data thatcan, over time, change (e.g., in RAM or cache).

Various examples have been described herein. Any combination of thedescribed operations or functions is contemplated. These and otherexamples are within the scope of the following claims.

What is claimed is:
 1. A method comprising: identifying, by processingcircuitry, an initial electrode combination configured to deliverelectrical stimulation therapy via a lead, the lead comprising aplurality of electrodes arranged in a complex electrode array geometry,wherein the initial electrode combination comprises one or moreelectrodes of the plurality of electrodes; determining, by theprocessing circuitry and based on the one or more electrodes of theinitial electrode combination, a plurality of alternative electrodecombinations for delivering electrical stimulation therapy, wherein eachalternative electrode combination of the plurality of alternativeelectrode combinations is different than the initial electrodecombination and is associated with a respective power consumption valuelower than a power consumption value associated with the initialelectrode combination; and receiving, via a user interface, user inputselecting one alternative electrode combination from any of theplurality of alternative electrode combinations for delivery ofelectrical stimulation therapy.
 2. The method of claim 1, furthercomprising controlling a medical device to deliver the electricalstimulation therapy according to the selected one alternative electrodecombination of the plurality of alternative electrode combinations. 3.The method of claim 1, further comprising outputting, for each of theinitial electrode combination and at least one of the plurality ofalternative electrode combinations, a visual representation of astimulation field deliverable via the respective electrode combination.4. The method of claim 1, further comprising calculating, for each ofthe plurality of alternative electrode combinations, a respective fieldsimilarity score indicating a similarity of a stimulation fielddeliverable by the respective electrode combination with respect to astimulation field deliverable by the initial electrode combination. 5.The method of claim 4, wherein calculating the respective fieldsimilarity scores comprises: determining an original stimulation fielddeliverable by the initial electrode combination; determining, for eachof the plurality of alternative electrode combinations, a respectivestimulation field deliverable by the respective alternative electrodecombination; comparing, for each of the plurality of alternativeelectrode combinations, the respective stimulation field deliverable bythe respective alternative electrode combination to the originalstimulation field deliverable by the initial electrode combination; andoutputting, for each of the plurality of alternative electrodecombinations, an indication of the comparison.
 6. The method of claim 4,further comprising outputting, for display, a representation of at leastone of the plurality of alternative electrode combinations for selectionin at least partially defining electrical stimulation therapy, therepresentation comprising an indication of at least one of therespective power consumption values or the respective field similarityscores.
 7. The method of claim 1, wherein the method further comprises:ranking the plurality of alternative electrode combinations based on therespective power consumption values; and outputting, for display, arepresentation of at least some of the plurality of alternativeelectrode combinations according to the ranking.
 8. The method of claim1, wherein each of the plurality of alternative electrode combinationscomprises a greater number of electrodes than the initial electrodecombination.
 9. The method of claim 1, wherein determining the pluralityof alternative electrode combinations comprises iteratively determiningeach of the plurality of alternative electrode combinations such thatsuccessive alternative electrode combinations add at least one electrodeto all electrodes defined by previously determined alternative electrodecombinations, and wherein the successive alternative electrodecombinations include electrodes at increasing distances from anelectrode of the initial electrode combination.
 10. The method of claim1, wherein: a first alternative electrode combination of the pluralityof alternative electrode combinations comprises a first number ofelectrodes less than or equal to a second number of electrodes of theinitial electrode combination; and a first power consumption valueassociated with the first alternative electrode combination is less thanthe power consumption value associated with the second number ofelectrodes of the initial electrode combination.
 11. The method of claim1, further comprising calculating the respective power consumptionvalues for the initial electrode combination and the plurality ofalternative electrode combinations by calculating, for the initialelectrode combination and the plurality of alternative electrodecombinations, power dissipation from at least one of an R-matrix, aZ-matrix, or an electrical model of a system delivering electricalstimulation using one of a common set of stimulation parameters ordifferent sets of stimulation parameters.
 12. The method of claim 1,wherein the electrical stimulation therapy comprises deep brainstimulation therapy.
 13. A system comprising: processing circuitryconfigured to: identify an initial electrode combination configured todeliver electrical stimulation therapy via a lead, the lead comprising aplurality of electrodes arranged in a complex electrode array geometry,wherein the initial electrode combination comprises one or moreelectrodes of the plurality of electrodes; determine, based on the oneor more electrodes of the initial electrode combination, a plurality ofalternative electrode combinations for delivering electrical stimulationtherapy, wherein each alternative electrode combination of the pluralityof alternative electrode combinations is different than the initialelectrode combination and is associated with a respective powerconsumption value lower than a power consumption value associated withthe initial electrode combination; and receive, via a user interface,user input selecting one alternative electrode combination from any ofthe plurality of alternative electrode combinations for delivery ofelectrical stimulation therapy.
 14. The system of claim 13, wherein theprocessing circuitry configured to control a medical device to deliverthe electrical stimulation therapy according to the selected onealternative electrode combination of the plurality of alternativeelectrode combinations.
 15. The system of claim 13, further comprising adisplay, wherein the processing circuitry is configured to control, foreach of the initial electrode combination and at least one of theplurality of alternative electrode combinations, the display to output avisual representation of a stimulation field deliverable via therespective electrode combination.
 16. The system of claim 13, whereinthe processing circuitry is configured to calculate, for each of theplurality of alternative electrode combinations, a respective fieldsimilarity score indicating a similarity of a stimulation fielddeliverable by the respective electrode combination with respect to astimulation field deliverable by the initial electrode combination. 17.The system of claim 16, further comprising a display, wherein theprocessing circuitry is configured to control the display to output arepresentation of at least one of the plurality of alternative electrodecombinations for selection in at least partially defining electricalstimulation therapy, the representation comprising an indication of atleast one of the respective power consumption values or the respectivefield similarity scores.
 18. The system of claim 13, wherein theprocessing circuitry is configured to: rank the plurality of alternativeelectrode combinations based on the respective power consumption value;and output, for display, a representation of at least some of theplurality of alternative electrode combinations according to theranking.
 19. The system of claim 13, wherein each of the plurality ofalternative electrode combinations comprises a greater number ofelectrodes than the initial electrode combination.
 20. The system ofclaim 13, wherein the processing circuitry is configured to determinethe plurality of alternative electrode combinations by iterativelydetermining each of the plurality of alternative electrode combinationssuch that successive alternative electrode combinations add at least oneelectrode to all electrodes defined by previously determined alternativeelectrode combinations, and wherein the successive alternative electrodecombinations include electrodes at increasing distances from anelectrode of the initial electrode combination.
 21. The system of claim13, wherein: a first alternative electrode combination of the pluralityof alternative electrode combinations comprises a first number ofelectrodes less than or equal to a second number of electrodes of theinitial electrode combination; and a first power consumption valueassociated with the first alternative electrode combination is less thanthe power consumption value associated with the second number ofelectrodes of the initial electrode combination.
 22. The system of claim13, further comprising: an external programmer that comprises a userinterface and the processing circuitry, wherein the external programmeris configured to: receive, via the user interface, the user inputselecting the one alternative electrode combination of the plurality ofalternative electrode combinations; and control, by the processingcircuitry, delivery of electrical stimulation therapy to a patientaccording to the selected one alternative electrode combination; and animplantable medical device configured to receive the selected onealternative electrode combination and deliver the electrical stimulationtherapy according to the selected one alternative electrode combination.23. The system of claim 13, wherein the electrical stimulation therapycomprises deep brain stimulation therapy.
 24. A system comprising: meansfor identifying an initial electrode combination configured to deliverelectrical stimulation therapy via a lead, the lead comprising aplurality of electrodes arranged in a complex electrode array geometry,wherein the initial electrode combination comprises one or moreelectrodes of the plurality of electrodes; means for determining, basedon the one or more electrodes of the initial electrode combination, aplurality of alternative electrode combinations for deliveringelectrical stimulation therapy, wherein each alternative electrodecombination of the plurality of alternative electrode combinations isdifferent than the initial electrode combination and is associated witha respective power consumption value lower than a power consumptionvalue associated with the initial electrode combination; and means forreceiving user input selecting one alternative electrode combination ofthe plurality of alternative electrode combinations for delivery ofelectrical stimulation therapy.